CN110382816A - Underground communica tion - Google Patents

Abstract

Downhole electrical energy collection and communication in systems for well installations with metal structures carrying electrical currents (eg, CP currents). In some cases, there is a collection module (4) electrically connected to the metal structure (2) at a first location and electrically connected to a second location spaced from the first location, the first location and The second position is chosen such that, in use, due to the current flowing in the structure (2), there is a potential difference between the first position and the second position; and the collection module (4) is arranged from This current collects electrical energy. Additionally or alternatively, there are communication devices (4, 5, 6) that communicate by modulating current (eg CP current) in the metal structure (2).

Description

downhole communication

The present invention relates to downhole communication. In particular, the present invention relates to methods and systems for communicating using devices in well installations having metal structures provided with cathodic protection. The present invention also relates to methods and systems incorporating energy harvesting methods and systems, and apparatus for use in such methods and systems.

It is often desirable to be able to extract data from oil and/or gas wells and control equipment in oil and/or gas wells, such as valves, eg, subterranean safety valves.

However, powering such downhole equipment is challenging. There are some situations where power can be provided directly from the ground via electrical cables or where hydraulic power can be used to power the device directly from the ground. However, in other situations these methods of power delivery are not appropriate. In some cases, using batteries becomes an option. However, this is inherently challenging, especially in downhole environments, where relatively high temperatures tend to result in shortened battery life.

Therefore, it is desirable to provide an alternative source to power downhole equipment that can be used in situations where delivering power directly from the surface via cable or hydraulically is difficult, impossible, or undesirable, while avoiding reliance on batteries power limitations will be encountered. It is also desirable to provide alternative methods for communicating between downhole locations and other downhole locations and/or surface locations.

In this specification, the expression "surface" includes the land surface where the well head in land wells will be located, the seabed/mud line in subsea wells, and the wellhead deck on the platform. It also contains positions above these positions, where appropriate. In general, "surface" is used to refer to, for example, any convenient location for applying and/or picking up power/signal that is outside the borehole of the well.

According to a first aspect of the present invention, there is provided a downhole electrical energy collection system for collecting electrical energy in a well installation having a metal structure carrying electrical current, the system comprising:

a collection module electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location being selected such that in use , there is a potential difference between the first position and the second position due to the current flowing in the structure; and the collection module is arranged to collect electrical energy from the current.

The well facility may be a cathodic protected well facility such that the current is a cathodic protection current. While the present technique can be used in systems that apply electrical current exclusively to the downhole structure for power delivery, it has been recognized that power can be harvested from a cathodic protection system, and it is particularly preferred if it can be harvested from an already existing current power.

The second location will typically be a downhole location.

In some cases, the connection to the second location may be a connection to the formation via the electrode. Most typically, however, the collection modules will be attached to the metal structure at first and second spaced apart locations.

Such systems and methods are advantageous because power can be provided to downhole equipment without having to provide a discrete power supply. Furthermore, power can be supplied without having to rely on local batteries, which tend to have limited lifetimes, and without having to provide cables penetrating the wellhead. Similarly, these techniques can be implemented without the use of toroidal coils to inject or extract signals. This reduces the complexity and technical issues that can arise when implementing the system.

The collection module may be arranged to collect electrical energy from the dc current.

Preferably, the current flow within the portions of the metal structure in the region between the first position and the second position is in the same longitudinal direction.

Preferably, there is an uninterrupted current flow path between the first position and the second position, the current flow path at least partially through the metal structure.

The characteristics these represent will generally exist in a facility unless the settings are modified. The idea generally does not require modification of the standard set-up of the well facility as a whole, ie they are designed to work with the standard facility.

The collection module may be electrically connected to the metal structure at the second location.

The or each connection to the metal structure may be formed to a length of metal elongated member/a length of metal pipe.

In one set of embodiments, the spaced-apart locations may be axially spaced apart. The connection may be formed to a common length of metal elongated member, such as a common length of metal pipe that is part of the metal structure. The uppermost of the two spaced-apart locations may be adjacent to the location of a liner hanger disposed in the well. Typically, this will represent the highest actual position for the topmost position. In some cases, the upper connection may be formed to a riser.

Thus, for example, both the connections may be formed to production tubing disposed in the well, or both may be formed to a first "A" annulus separated from the production tubing by a first "A" annulus A length of casing, or both, may be formed to a second length of casing separate from the first length of casing through a second "B" annulus, or so on.

In other cases, the axially spaced connections may be formed to different lengths of metal elongated members, such as different lengths of metal pipe with similar results, but it is often more convenient to form the connections to Metal slender members/metal tubes of the same length, if there is no reason to change.

Where the spaced locations are axially spaced and there is a potential difference between them depending on this, the separation between the locations may be quite large, typically 100m or more. More preferably it is 300m to 500m.

The electrical connection to the metal structure at the first location may be a galvanic connection.

The electrical connection to the metal structure at the second location may be a galvanic connection.

The collection module may be positioned in one or more of: outside the well elongated member, within the annulus of the well, and within the bore of the well.

The connection to at least one of the first position and the second position may be via a cable extending alongside the metal structure.

Preferably, if the second spaced-apart contacts are formed to the at least one length of the metal elongated member, the current flowing in the at least one length of the metal elongated member at the location where the first contact is formed is the same as when the second contact is formed The current flowing in the at least one piece of the metal elongated member flows in the same longitudinal direction.

Preferably, if both the first spaced-apart contacts and the second spaced-apart contacts are formed to the same length of metal elongated member, the length of metal elongated member is in the first and second positions conduct electricity continuously.

The at least one connection between at least one of the electrical contacts and the collection module may be provided by an insulated cable.

The cable may be selected to have conductors with a relatively large cross-sectional area. When selecting a cable, the aim is to pick a cross-sectional area large enough to allow the desired level of collection that provides a sufficiently low electrical resistance in the cable.

Preferably, the insulated cable has a conductive area of at least 10mm^2, preferably at least 20mm^2, more preferably at least 80mm^2.

The cable may be a tubing encapsulated conductor.

One of the connections may be formed without an external cable. One of the connections may be formed via or surrounding the conductive housing of the collection module.

Typically, there will be optimal spacing between the connections. The greater the spacing, the greater the change in potential between the contact locations, but also the greater the resistance of the cable. The method may include determining optimal spacing between the spaced locations. This can be determined by modeling a specific facility.

The spacing between the positions may be at least 100 m.

In another set of embodiments, the spaced-apart locations may be radially spaced apart. A first of the connections may be formed to a first length of metal elongated member, such as a first length of metal pipe that is part of the metal structure, and a second of the connections may be formed to a different first. A two-section metal elongated member, such as a different second-section metal tube that is part of the metal structure. Thus, the connection may span the annulus defined by the two lengths of metal pipe.

For example, a connection may be formed to production tubing disposed in the well and a connection may be formed to a first segment of casing that is separate from the production tubing by a first "A" annulus, or a connection may be formed to A first length of casing is provided in the well and a connection is formed to a second length of casing separated from the first length of casing by a second "B" annulus, and so on.

In some cases, the spaced-apart locations may be both axially spaced and radially spaced.

The connections may be formed to a common length of metal elongated member that is part of the metal structure.

In some embodiments, a first of the connections is formed to a first segment of metal elongated member that is part of the metal structure, and a second of the connections is formed to be the A different second segment metal elongated member that is part of the metal structure.

Insulation means may be provided for electrically insulating the first length of metal elongated member from the second length of metal elongated member in the region of the connection portion.

Insulation means may be provided for electrically insulating the first length of elongated member/metal tube from the second length of elongated member/metal tube in the region of at least one of the connections. This can help to ensure that there is a potential difference between the length of elongated member/metal tube at the point where the connection is formed. This is due to the different paths to ground that exist from each length of member/pipe.

Note that in the present technology, the current (from which energy is harvested) will generally flow in the same direction in the first and second lengths of metal elongated member/tube. Thus, the insulation is not arranged to form a separate return path, but rather modifies the path to ground of one of the segments relative to the other.

The insulating means may comprise an insulating layer or coating provided on at least one of the lengths of elongated member/metal tube. The insulating means may comprise at least one insulating centraliser for keeping the lengths of elongated member/metal tube separated from each other.

The insulating means may be arranged to avoid electrical contact between the two lengths of elongated member/metal pipe for a distance of at least 100m, preferably at least 300m.

At least one of the connections may be positioned within the insulating area. Both of the connections may be positioned in the insulating area. At least one of the connecting portions may be positioned towards the midpoint of the insulating area. The location of at least one of the connections may be determined by modeling a particular facility to determine an optimal location that is then selected.

The collection module may be placed in the bore of a central section of tubing, in the annulus, or outside the casing - between the casing and the formation. Thus, among other possible locations, the collection module may be positioned in the "A" annulus, the "B" annulus, the "C" annulus, the "D" annulus, or any other annulus.

This creates the possibility of supplying power in locations where it is often not possible and/or desirable to place cables from the ground. This is especially useful for subsea wells. Furthermore, this is possible without relying on the use of a primary battery or another local power source, so there is the possibility of providing "well life" power in such a location.

The collection module may comprise variable impedance means for varying the load present between the two connections. The variable impedance device may be microprocessor controlled.

The variable impedance device can be used to vary the load in order to optimize energy harvesting.

The variable impedance device can be used to modulate the load to communicate data from the collection module towards the ground.

The downhole communication device may be arranged to transmit data from downhole to the surface. The downhole communication device may also be arranged to receive data eg from the surface.

The collection module may include a downhole communication device. In other cases, the downhole communication device may be provided discretely. Downhole equipment powered by the collection module may include the downhole communication device.

The downhole communication device may include the variable impedance device.

The upper communication device may be provided at a location outside the eyelet, including a detector for detecting changes in current (eg, cathodic protection current) flowing in the metal structure, thus allowing extraction through the load at the collection module modulation of the encoded data. For example, the detector may be arranged to detect the potential of the metal structure relative to a reference, or to detect the potential present across a power supply used to apply an applied cathodic protection current to the metal structure, or to detect the potential present across a power supply used to apply an applied cathodic protection current to the metal structure. The current present in the power supply of the applied cathodic protection current is applied to the metal structure.

In other embodiments, instead of modulating the load to communicate towards the ground, other communication techniques may be used. Typically, for example, acoustic signaling and/or EM (electromagnetic) signaling may be used. A modulated load is one example of EM signaling, but other, more direct means of EM signaling can be used.

The downhole communication device may be arranged to apply signal-bearing acoustic data to the metal structure, and the upper communication device may be arranged to receive signal-bearing acoustic data.

The downhole communication device may be arranged to apply signal-bearing EM (electromagnetic) data to the metal structure, and the upper communication device may be arranged to receive signal-bearing EM data.

The topside communication device may be arranged to apply signal-bearing acoustic and/or EM (electromagnetic) data to the metal structure, and the downhole communication device may be arranged to receive signal-bearing acoustic and/or EM data.

In some cases, the topside communication device and the downhole communication device may be arranged to communicate using both acoustic and EM signals. This creates useful redundancy because if one communication channel fails, the other communication channel can remain operational.

The collection module may be arranged at a selected downhole location for collecting power, and a cable may be arranged for further supplying electrical power downhole to downhole equipment. The cross-sectional area of cables used to supply electrical power further downhole will typically be smaller than that of any cables used in harvesting power, and will typically be slower than due to the current flowing in the metal structure (eg, due to cathodic protection current) and supply power further down at a higher voltage developed across the spaced contacts.

In some embodiments, the electrical current flowing in the elongated member is supplied from the surface of the well.

In some embodiments, the electrical current flowing in the elongated member is supplied from one or more sacrificial anodes.

In some embodiments, the current flowing in the elongated member is an impressed current from an external power supply.

In some embodiments, the voltage at the ground of the well is limited in use to a range of minus 0.7 volts to minus 2 volts relative to a silver/silver chloride reference cell.

Preferably, the potential difference between the spaced contacts is less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

Optionally, the resistance of the well structure between the contacts is less than 0.1 ohm, preferably less than 0.01 ohm.

The optimal location for harvesting power will typically be near the location where current (eg, cathodic protection current) is injected into the metal structure.

Where the spaced-apart locations are axially spaced apart, preferably, the upper location is adjacent to where current (eg, cathodic protection current) is injected into the metal structure. Note that in the presence of a platform structure, electrical current (eg, cathodic protection current) may reach the downhole metal structure via the galvanic connection to the platform structure. In some cases, the present technique may include controlling the position of the connection.

The best location for harvesting power will often be near the wellhead, where there is a maximum rate of potential change when advancing further down the well. On the other hand, the downhole equipment to be powered may be further downhole. Thus, the collection module and downhole equipment may be at different locations in the well, especially at different depths.

In other cases, the collection module and downhole equipment may be positioned together. The system may include a downhole unit including the collection module and the downhole equipment.

The upper spaced contacts may be:

where the well is a land well, within 100m, preferably within 50m of the land surface; and

Where the well is a subsea well, within 100m of the mudline, preferably within 50m of the mudline.

The upper spaced-apart contacts may be positioned adjacent to a location corresponding to the maximum value of the potential magnitude caused by the current flowing in the structure.

The system may also include downhole communication means for transmitting and/or receiving data.

The downhole communication device may be arranged to transmit data by varying the load present between the connections at the spaced-apart locations.

According to another aspect of the present invention there is provided a downhole equipment operating system comprising a downhole electrical energy collection system as defined above and a downhole equipment, the collection module being electrically connected to the downhole equipment and being arranged for supplying power to the downhole equipment.

The downhole equipment may include downhole sensors, such as pressure sensors and/or temperature sensors. The sensor may be mounted in, for example, an "A" annulus, a "B" annulus, a "C" annulus, or a "D" annulus.

A sensor arranged in one annulus or hole may be arranged to monitor a parameter in an adjacent annulus or hole, and or alternatively, to monitor a parameter in the annulus or hole in which it is located. Ports can be placed through a length of metal structure to allow sensing in an adjacent annulus or hole.

The sensor may be arranged to detect leaks in the cemented annulus.

The sensor may comprise an array of sensors.

The downhole equipment may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The communication module may include a downhole communication repeater. This downhole communication repeater may be a repeater for acoustic communication, or EM communication including wireless EM communication and cable borne EM communication, or for a hybrid communication system. For example, the transponder may receive acoustic signals from further downhole and transmit signals towards the surface using EM communications, or vice versa. Similarly, both acoustic communication and EM communication can be used in one or both directions. EM signal transmission can be achieved by applying an electrical signal downhole or modulating the load in the collection module as described above. The EM signal transmission may be at least partially along the cable, as mentioned above.

Where the downhole equipment is a repeater or transceiver, the system may be pre-installed in the well facility to make the well "wireless ready". That is, the system can be installed to provide a wireless communication backbone even though the communication capability may not be used initially. Here again, wireless refers to the presence of at least one wireless leg in the communication channel, other legs may be via cables.

In other cases, the system can be retro-fit.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

Note that each device may be a remote control device, which may be a wireless control device, eg in the sense that there is at least one wireless branch in the communication channel in the case of control from the ground. Other branches may be via cables, eg between the sensor location and the collection location.

EM signalling can use either dc or ac signals and an appropriate modulation scheme. The harvesting module may include a dc-dc converter for harvesting power from cathodic protection current or other currents present. The harvesting module may include an energy storage device for storing the harvested power. The energy storage device may include a charge storage device, which may include at least one capacitor and/or at least one rechargeable battery. In the presence of energy storage means, the harvesting module may be arranged to selectively supply power from the storage device or directly from the harvested energy. This selection can be made based on predetermined conditions. Alternatively, there may be no energy storage device present, and the harvesting module may be arranged to supply power continuously when needed.

A primary battery may also be provided at the collection module for selective use.

The dc-dc converter may comprise a field effect transistor arranged to form a resonant boost oscillator. The dc-dc converter may include a step-up transformer, and may include a coupling capacitor.

The collection module may be arranged to control the turns ratio of the step-up transformer to modify the load generated by the dc-dc converter. The secondary winding of the boost transformer may comprise multiple taps and/or the boost transformer may comprise multiple secondary windings, and the collection module may be arranged to select windings and/or taps to provide the desired turns number ratio. Microprocessor controlled switches can be used to select taps and/or windings.

According to another aspect, there is provided a downhole unit comprising a collection module as defined above and at least one device arranged to be powered by the collection module.

One or more of the sensor module, communication module, and collection module may be disposed in an annulus such as a "B" annulus or a "C" annulus or another annulus. The sensor module and the collection module may be provided as part of a common downhole unit, however more typically they will be discrete so that the sensor can be positioned deeper than the collection module.

Downhole equipment may be located in the well at a different location than the collection module.

Collection modules may be arranged at selected downhole locations for collecting power, and cables may be arranged for further supplying electrical power downhole to downhole equipment at various locations in the well.

The cross-sectional area of the one or more conductive cores of the cable used to supply electrical power further downhole may be smaller than the cross-sectional area of the one or more conductive cores of the cable used to connect the collection module to the downhole structure for collecting power.

According to another aspect of the present invention, there is provided a downhole well monitoring system for monitoring at least one parameter in a well installation having a metal structure carrying electrical current, the system comprising:

an electrical energy harvesting system as defined above;

a sensor module for sensing at least one parameter; and

a communication module to send data encoding the readings from the sensor module towards the ground,

The electrical energy harvesting system is arranged to supply electrical power to at least one of the sensor module and the communication module.

According to another aspect of the present invention, there is provided a downhole well monitoring system for monitoring at least one parameter in a well installation having a metal structure carrying electrical current, the system comprising:

a sensor module for sensing at least one parameter;

a communications module for sending data encoding readings from the sensor module towards the ground; and

An electrical energy harvesting system including a harvesting module electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location The two positions are chosen such that, in use, due to the current flowing in the structure, there is a potential difference between the first position and the second position; and, the collection module is arranged to collect electrical energy from the current, the An electrical energy harvesting system is arranged to supply electrical power to at least one of the sensor module and the communication module.

The system may include at least one first length of cable for connecting the collection module to one of the spaced-apart locations.

The system may include at least one second length of cable for supplying power from the collection module to the sensor module.

The cross-sectional area of the conductive portion of the first length of cable may be greater than the cross-sectional area of the conductive portion of the second length of cable.

The communication module may be arranged to modulate the current flowing in the metal structure at the signal transmission location in order to encode data to allow for the modulation of current at the reception location remote from the signal transmission location by detecting said modulation influence to extract the data at the receiving location.

The well monitoring system may include a detector for detecting the effect of the modulation on the current at the receiving location, thereby extracting encoded data.

The communication module may be arranged to control the load generated by the collection module to produce said modulation of the current in the metal structure at the signal transmission location.

The sensor module may include a pressure sensor.

The pressure sensor may be arranged to monitor the reservoir pressure of the well.

The pressure sensor may be arranged to monitor the pressure in the annulus of the well.

The pressure sensor may be arranged to monitor the pressure in the closed annulus of the well.

According to another aspect of the present invention, there is provided a downhole communication repeater system for use in a well installation having a metal structure carrying electrical current, the system comprising:

an electrical energy harvesting system as defined above; and

a communication repeater arranged in the well and downhole and arranged to communicate with a first device beyond the wellhead using at least a wireless communication channel through the wellhead and arranged to communicate with the first device positioned in the well so as to be at the wellhead The second device below communicates such that the communication repeater can act as a repeater between the first device and the second device, the power harvesting system being arranged to supply electrical power to the communication repeater.

According to another aspect of the present invention, there is provided a downhole communication repeater system for use in a well installation having a metal structure carrying electrical current, the system comprising:

a communication repeater arranged in the well and downhole and arranged to communicate with a first device beyond the wellhead using at least a wireless communication channel through the wellhead and arranged for communication with a first device positioned in the well to thereby The second equipment communicates below the wellhead such that the communication repeater can act as a repeater between the first equipment and the second equipment; and

An electrical energy harvesting system including a harvesting module electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location the position is selected such that, in use, there is a potential difference between the first position and the second position due to the current flowing in the structure; and the collection module is arranged to collect electrical energy from the current, the electrical energy collecting The system is arranged to supply electrical power to the communication repeater.

It should be understood that references herein to a first device beyond the wellhead refer to devices on the other side of the wellhead than the second device in the well, such that communication across the wellhead is desired. Ultimately, the first device can be positioned in almost any location, be it close to the wellhead or at a remote location, as long as appropriate communications are set up.

The communication repeater may be arranged to modulate the current flowing in the metal structure at the signal transmission location in order to encode the data to allow by detecting the effect of said modulation on the current at the reception location remote from the signal transmission location to extract the data at the receiving location.

The communication repeater and/or the collection module may be disposed in an annulus such as a "B" annulus or a "C" annulus or another annulus.

The communication repeater and the collection module may be provided as part of a common downhole unit.

The system may include at least one first length of cable for connecting the collection module to one of the spaced-apart locations.

The system may include at least one second length of cable for supplying power from the collection module to the communication repeater.

The cross-sectional area of the conductive portion of the first length of cable may be greater than the cross-sectional area of the conductive portion of the second length of cable.

The downhole communication repeater system may include a detector for detecting the effect of the modulation on the current at the receiving location to extract encoded data.

The communication repeater may be arranged to control the load generated by the collection module to cause said modulation of the current in the metal structure at the signal transmission location.

According to another aspect of the present invention, there is provided a downhole equipment operating system for operating downhole equipment in a well installation having a metal structure carrying electrical current, the system comprising:

a downhole equipment;

An electrical energy harvesting system including a harvesting module electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location the position is selected such that, in use, there is a potential difference between the first position and the second position due to the current flowing in the structure; and the collection module is arranged to collect electrical energy from the current, the electrical energy A collection system is arranged to supply electrical power to the downhole equipment.

The downhole equipment may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

Power can be supplied to control the valve, where the power to move the valve comes from another source (eg, spring loaded, differential pressure), or supplied to move the valve or to control and move the valve. The valve may include a trigger mechanism, such as a pilot valve that uses power from a power delivery system to operate it.

The device operating system may be arranged to supply variable power levels. Thus, the first power level may be provided except when a second, higher power level is required. When higher power levels are required, the applied current can be increased by plugging in more anodes or applying a higher impressed current, eg cathodic protection current. This may be at a level that is undesirable in the long term but acceptable in the short term due to the potentially damaging effects of too high a potential difference caused by the cathodic protection current - hydrogen embrittlement. Thus, the system, apparatus, method may be arranged to temporarily increase the applied current, eg cathodic protection current. Higher power levels may be used, for example, to move a valve from one state to another, while lower levels are used at other times, such as monitoring and/or control signals.

The downhole equipment may be positioned in the well at a different location than the collection module.

The collection module may be arranged downhole at selected locations for collecting power, and a cable is provided for further supplying electrical power downhole to the downhole equipment at various locations in the well.

The cross-sectional area of one or more conductive cores of the cable used to further supply electrical power downhole may be smaller than the cross-sectional area of one or more conductive cores of the cable used to connect the collection module to the downhole structure for power collection. Sectional area.

In addition to the electrical power supplied by the electrical energy harvesting module, another source of power may be available to the downhole equipment.

In each of the above instruments, the collection module may comprise variable impedance means for varying the load present between the two connections. The variable impedance device may be microprocessor controlled.

The variable impedance device can be used to vary the load in order to optimize energy harvesting.

The variable impedance device can be used to modulate the load to communicate data from the collection module towards the ground.

Impedance modulation can also be used in communication from the upper location towards the collection module in order to modulate the applied (eg cathodic protection) current. One possibility is to switch the anode in and out of operation, which will modulate the potential present downhole. Thus, data can be encoded by operating the anode in and out of operation. For example, the connection between the anode and the structure can be selectively made and broken by a switching device. Thus, the upper communication unit may comprise switching means for switching the anode in and out of operation. In an impressed current system, the applied signal can be modulated to encode data.

According to another aspect of the present invention, there is provided a method of powering downhole equipment in a well installation having a metal structure carrying electrical current, the method comprising the steps of:

electrically connecting a collection unit to the metal structure at a first location and to a second location spaced from the first location, the first location and the second location being selected such that due to flow in the structure current, so there is a potential difference between the first position and the second position, and the collection unit is arranged to collect electrical energy from the current when connected between the positions with the potential difference;

collecting electrical power from the current at a collection unit; and

The downhole equipment is supplied with electrical power from the collection unit.

The method may include the steps of: determining a location where a maximum value of the magnitude of the potential caused by the current flowing in the structure exists; and selecting the first connection connecting the collection unit to the metal structure according to the location of the maximum value a location.

According to another aspect of the present invention, there is provided a downhole electrical energy collection system for use in a well facility having a metal structure including at least a section of a metal elongated member that carries electrical current, the collection system comprising : an energy harvesting module comprising an electrical circuit connected between the spaced contacts to harvest energy from the potential difference between the spaced contacts, wherein the spaced contacts A first one of the contacts is formed to the at least one length of metal elongated member at a first location, and a second one of the spaced contacts is formed to the at least one segment at a second location a metallic elongate member, and the potential difference is caused by the current flowing in the at least one segment of the elongated member and at least in part by the impedance of the at least one segment of the elongated member.

The current flowing in the at least one length of metal elongated member at the location where the first contact is formed may be in the same longitudinal direction as the current flowing in the at least one length of metal elongated member at the location where the second contact is formed flow in the direction.

Preferably, if both the first spaced-apart contacts and the second spaced-apart contacts are formed to the same length of metal elongated member, the length of metal elongated member is between the first and second positions conduct electricity continuously.

Preferably, the metal structure provides an uninterrupted current flow path between the first position and the second position.

Preferably, the current flow within the portions of the metal structure in the region between the first and second positions is in the same longitudinal direction.

Preferably, the collection module is arranged to collect electrical energy from the dc current.

The electrical connection to the metal structure at the first location may be a galvanic connection.

The electrical connection to the metal structure at the second location may be a galvanic connection.

The electrical connection to the metal structure at the first location may be made to one of: casing, liner, tubing, coiled tubing, sucker rod.

The electrical connection to the metal structure at the second location may be made to one of: casing, liner, tubing, coiled tubing, sucker rod.

The spaced-apart locations may be axially spaced apart.

The spaced-apart locations may be radially spaced apart.

At least one connection between at least one of the electrical contacts and the circuit may be provided by an insulated cable.

Preferably, the insulated cable has a conductive area of at least 10mm^2, preferably at least 20mm^2, more preferably at least 80mm^2.

The cable may be a tubing encapsulated conductor.

The spacing between the positions may be at least 100 m.

The connections may be formed to a common length of metal elongated member that is part of the metal structure.

In some embodiments, a first of the connections is formed to a first segment of metal elongated member that is part of the metal structure, and a second of the connections is formed to be the A different second segment metal elongated member that is part of the metal structure.

Insulation means may be provided for electrically insulating the first length of metal elongated member from the second length of metal elongated member in the region of the connection portion.

The insulating means may comprise an insulating layer or coating disposed on at least one of the segment metal elongate members.

The insulating means may include at least one insulating centralizer for keeping the segments of metal elongated members apart from each other.

The insulating means may be arranged to avoid electrical contact between the two lengths of metal elongated member for a distance of at least 100 m.

The electrical current flowing in the elongated member may be supplied from the surface of the well.

The electrical current flowing in the elongated member may be supplied from one or more sacrificial anodes.

The current flowing in the elongated member may be an impressed current from an external power supply.

The voltage at the ground of the well can be limited in use to the range of minus 0.7 volts to minus 2 volts relative to the silver/silver chloride reference cell.

The potential difference between the spaced contacts may be less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

The resistance of the well structure between said contacts may be less than 0.1 ohm, preferably less than 0.01 ohm.

The upper spaced contacts may be:

where the well is a land well, within 100m, preferably within 50m of the land surface; and

Where the well is a subsea well, within 100m of the mudline, preferably within 50m of the mudline.

The upper spaced-apart contacts may be positioned adjacent to a location corresponding to the maximum value of the magnitude of the potential caused by the current flowing in the structure.

The system may include downhole communication means for transmitting and/or receiving data.

The downhole communication device may be arranged to transmit data by varying the load detected between the connections at the spaced locations.

According to another aspect of the present invention there is provided a downhole equipment operating system comprising a downhole electrical energy collection system as defined above and a downhole equipment, the collection module being electrically connected to the downhole equipment and being arranged for supplying power to the downhole equipment.

The downhole equipment may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

The downhole equipment may be positioned in the well at a different location than the collection module.

The collection module may be arranged downhole at selected locations for collecting power, and a cable may be provided for further supplying electrical power downhole to the downhole equipment at various locations in the well.

The cross-sectional area of one or more conductive cores of the cable used to further supply electrical power downhole may be smaller than the cross-sectional area of one or more conductive cores of the cable used to connect the collection module to the downhole structure for collecting electrical power. Sectional area.

According to another aspect of the present invention, there is provided a method of powering downhole equipment in a well installation having a metal structure carrying electrical current, the method comprising the steps of:

a collection unit is electrically connected to the metal structure at a first location and is electrically connected to the metal structure at a second location spaced from the first location, the first location and the second location being selected such that, There is a potential difference between the first position and the second position due to the current flowing in the structure, and the collection unit is arranged to collect electrical energy from the current when connected between the positions with the potential difference;

collecting electrical power from the current at a collection unit; and

The downhole equipment is supplied with electrical power from the collection unit.

The method may include the further steps of: determining a location where there is a maximum in the magnitude of the potential caused by the current flowing in the structure; and selecting a collector unit to connect the collection unit to the metal structure based on the location of the maximum the first position.

According to another aspect of the present invention, there is provided a downhole electrical energy collection system that collects electrical energy in a well facility having a metal structure provided with cathodic protection, the system comprising:

a collection module electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location being selected such that, in use, There is a potential difference between the first position and the second position due to the cathodic protection current flowing in the structure; and

The collection module is arranged to collect electrical energy from the cathodic protection current.

The collection module may be arranged to collect electrical energy from the dc current.

Current flow within portions of the metal structure in the region between the first and second positions may be in the same longitudinal direction.

There may be an uninterrupted current flow path between the first position and the second position, the uninterrupted current flow path at least partially through the metal structure.

The collection module may be electrically connected to the metal structure at the second location.

The spaced-apart locations may be axially spaced apart.

The spaced-apart locations may be radially spaced apart.

At least one connection between at least one of the electrical contacts and the collection module may be provided by an insulated cable.

The insulated cable has a conductive area of at least 10 mm^2, preferably at least 20 mm^2, more preferably at least 80 mm^2.

The cable may be a tubing encapsulated conductor.

The spacing between the positions may be at least 100 m.

The connections may be formed to a common length of metal elongated member that is part of the metal structure.

A first of the connections may be formed to a first segment of the metal elongated member as part of the metal structure, and a second of the connections may be formed to be part of the metal structure of different second segment metal elongated members.

Insulation means may be provided for electrically insulating the first length of metal elongated member from the second length of metal elongated member in the region of the connection portion.

The insulating means may comprise an insulating layer or coating disposed on at least one of the segment metal elongate members.

The insulating means may include at least one insulating centralizer for keeping the segments of metal elongated members apart from each other.

The insulating means may be arranged to avoid electrical contact between the two lengths of metal elongated member for a distance of at least 100 m.

The electrical current flowing in the elongated member may be supplied from the surface of the well.

The electrical current flowing in the elongated member may be supplied from one or more sacrificial anodes.

The current flowing in the elongated member may be an impressed current from an external power supply.

The voltage at the ground of the well can be limited in use to the range of minus 0.7 volts to minus 2 volts relative to the silver/silver chloride reference cell.

The potential difference between the spaced contacts may be less than 1 volt, preferably less than 0.5 volt, more preferably less than 0.1 volt.

The resistance of the well structure between said contacts may be less than 0.1 ohm, preferably less than 0.01 ohm.

The upper spaced contacts may be:

where the well is a land well, within 100m, preferably within 50m of the land surface; and

Where the well is a subsea well, within 100m of the mudline, preferably within 50m of the mudline.

The upper spaced-apart contacts may be positioned adjacent to a location corresponding to the maximum value of the magnitude of the potential caused by the current flowing in the structure.

The system may also include downhole communication means for transmitting and/or receiving data.

The downhole communication device may be arranged to transmit data by varying the load present between the connections at the spaced locations.

According to another aspect of the present invention there is provided a downhole equipment operating system comprising a downhole electrical energy collection system as defined above and a downhole equipment, the collection module being electrically connected to the downhole equipment and being arranged for supplying power to the downhole equipment.

The downhole equipment may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

The downhole equipment may be positioned in the well at a different location than the collection module.

The collection module may be arranged downhole at selected locations for collecting power, and a cable may be provided for further supplying electrical power downhole to the downhole equipment at various locations in the well.

The cross-sectional area of one or more conductive cores of the cable used to further supply electrical power downhole may be smaller than the cross-sectional area of one or more conductive cores of the cable used to connect the collection module to the downhole structure for collecting electrical power. Sectional area.

According to another aspect of the present invention, there is provided a downhole data communication apparatus for use in a well installation having a metal structure provided with a cathodic protection system such that there is a The electrical circuit of the metal structure and a ground return around which current flows due to the cathodic protection system, the downhole data communication device includes:

a first communication module positioned at a first location and comprising modulation means for modulating current at the first location to encode data; and

A second communication module positioned at a second location spaced from the first location and comprising a detector for detecting the effect of modulating the current at the first location in order to extract the data.

The modulation means may be arranged to be at least one of the following:

i) where the cathodic protection system is an external cathodic protection system, controlling the signal source of the external cathodic protection system to directly modulate the cathodic protection current applied to the metal structure;

ii) modifying the connection between at least one anode of the cathodic protection system and the metal structure; and

iii) Change the impedance of this circuit.

The first communication module may be arranged for positioning downhole.

The second communication module may be arranged for positioning downhole.

The apparatus may comprise a sensor module for sensing at least one parameter, wherein the first communication module is arranged for sending data encoding readings from the sensor module towards the second communication module.

The sensor module may include a pressure sensor.

The second communication module may be arranged to provide data to the downhole apparatus based on data received from the first communication module via the second communication module.

The downhole equipment may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

At least one of the first communication module and the second communication module may comprise a communication repeater for positioning in the well downhole and arranged to communicate with beyond the wellhead using at least a wireless communication channel through the wellhead The first device is in communication and is arranged to communicate with a second device positioned in the well and thus below the wellhead so that the communication repeater can act as a repeater between the first device and the second device.

The instrument may include a downhole electrical power harvesting module arranged for electrical connection between two spaced-apart locations in the well facility and an electrical circuit arranged for use in use The electrical energy is collected from a potential difference between the spaced locations for collection, the potential difference serving as an input voltage, the collection module being arranged for supplying power to at least one component of the communication device.

The first communication module may be arranged to control the load generated by the collection module to produce said modulation of the current in the metal structure at the signal transmission location.

The collection module may be arranged to collect electrical energy from the dc current.

According to another aspect of the present invention, there is provided a downhole data communication system comprising a downhole data communication apparatus as defined above positioned in a metal structure having a metal structure provided with cathodic protection well facility.

According to another aspect of the present invention there is provided a downhole data communication system for use in a well installation having a metal structure provided with a cathodic protection system such that there is an electrical circuit comprising the metal structure and a A ground return, around which current flows due to the cathodic protection system, the system comprising a downhole data communication apparatus comprising:

a first communication module positioned at a first location and comprising modulation means for modulating current at the first location to encode data; and

A second communication module positioned at a second location spaced from the first location and including a detector for detecting the effect of modulating the current at the first location for extraction the data.

The instrument may include a downhole electrical power harvesting module electrically connected between two spaced-apart locations in the well facility and an electrical circuit arranged to, in use, The electrical energy is collected at a potential difference between the collected spaced locations, the potential difference serving as an input voltage, the collection module being arranged to supply power to at least one component of the communication device.

The current flow within the portions of the metal structure in the region between the spaced locations for collection may be in the same longitudinal direction.

There may be an uninterrupted current flow path between the spaced locations for collection, the uninterrupted current flow path at least partially through the metal structure.

At least one of the first communication module and the second communication module may be positioned in the closed annulus of the well.

The system or apparatus may include a pressure sensor arranged to monitor the reservoir pressure of the well.

The system or instrument may include a pressure sensor arranged to monitor the pressure in the annulus of the well.

The system or apparatus may include a pressure sensor arranged to monitor the pressure in the closed annulus of the well.

According to another aspect of the present invention, there is provided a downhole electrical power harvesting module arranged for electrical connection between two spaced-apart locations in a well facility and comprising an electrical circuit that is arranged for harvesting, in use, electrical energy from a potential difference between the spaced locations, the potential difference serving as an input voltage.

The collection module may be arranged to collect electrical energy from the dc current.

The harvesting module may include control means for modifying the input impedance of the circuit to match the source impedance of the circuit to optimize power conversion efficiency.

The circuit may include a dc-dc converter.

The dc-dc converter may be arranged to operate with an input voltage above a minimum threshold, wherein the minimum threshold is not greater than 0.5 volts, preferably the minimum threshold is not greater than 0.25 volts, and more preferably the minimum threshold is not greater than 0.05 volts .

The dc-dc converter may include self-starting means to allow energy harvesting to be started when the available input voltage is below the semiconductor bandgap voltage of the components in the dc-dc converter.

The dc-dc converter may include self-starting means to allow energy harvesting to be started when the available input voltage is below 0.5 volts.

The dc-dc converter may include a step-up transformer.

The self-starting means may comprise a field effect transistor arranged with the boost transformer to form a resonant boost oscillator.

The dc-dc converter may comprise an H-bridge of transistors arranged under the control of control means for providing an input to the step-up transformer, and the self-starting means may comprise means for the control to allow start-up auxiliary power source.

The collection module may comprise control means arranged to control the turns ratio of the step-up transformer to modify the load generated by the dc-dc converter.

The secondary winding of the boost transformer may comprise a plurality of taps and/or the boost transformer may comprise a plurality of secondary windings and the control means may be arranged to select the windings and/or the taps to provide the desired turns ratio. The collection module may include at least one pair of terminals from which connections may be formed to two spaced-apart locations.

The collection module may have more than two terminals, wherein each of the terminals is used to allow connection to a corresponding location, and the collection module may also include switching means for selectively switching two of the terminals Electrical connections are made across the circuit, allowing selection of between which of the respective locations the circuit is connected.

This allows an arrangement where multiple contacts can be made with the metal structure during and after installation, a choice being made as to which contacts should be used. Thus, for example, the arrangement may comprise one lower connection and two upper connections at different locations. Once installed, it can be determined that if a first of the upper connections is used, more power can be harvested, so this first connection can be used. In another case, the second upper connection may be better.

The switch can also be used dynamically in use to switch between connections.

In another case, there may be two lower connections and or instead of two upper connections, or there may be other numbers of upper and/or lower connections.

The harvesting module may include an energy storage device for storing the harvested power. The energy storage device may include a charge storage device, which may include at least one capacitor and/or a rechargeable battery. The collection module may comprise variable impedance means for varying the load present between the two connections.

The variable impedance device may be microprocessor controlled.

The harvesting module may be arranged to vary the load using the variable impedance device in order to optimize energy harvesting.

The collection module may be arranged to modulate the load using the variable impedance device in order to communicate data away from the collection module.

The harvesting module may include a primary battery such that in use power can be selectively drawn from the power collected through the circuit and from the primary battery.

According to another aspect of the present invention there is provided a downhole tool comprising a collection module as defined above and a downhole device receiving power from the collection module.

The downhole tool may include a charge storage device and a power control device to control power to the downhole device when sufficient energy is available to power the device.

The downhole tool may include impedance modulation means for varying the input impedance of the collection module to modulate the load to transmit data from at least one of the electrical power collection unit and the downhole equipment.

The downhole tool may include modulation means for applying a modulated voltage via the spaced connections for transmitting data.

The downhole tool may include a primary battery such that, in use, power can be selectively drawn from the collected power and the primary battery.

The downhole equipment of the downhole tool may include at least one of the following:

Downhole sensors;

Downhole actuators;

annular sealing equipment, such as packers or packer elements;

valve;

Downhole communication modules such as transceivers or repeaters.

The valve may include at least one of the following:

underground safety valve;

Orifice flow control valve;

orifice to annulus valve;

annulus to annulus valve;

orifice to pressure compensation chamber valve;

Annulus to pressure compensation chamber valve;

Through packer or packer bypass valve.

According to another aspect of the present invention, there is provided a downhole electrical energy harvesting system for harvesting electrical energy in a well installation having a metal structure carrying an electrical current, the system comprising:

A collection module as defined above electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location being selected to be such that, in use, there is a potential difference between the first position and the second position due to the current flowing in the structure; and

The collection module is arranged to collect electrical energy from the current.

According to another aspect of the present invention, there is provided a downhole power delivery system for powering downhole equipment in a well installation having a metal structure carrying electrical current, the system comprising:

A collection module as defined above electrically connected to the metal structure at a first location and electrically connected to a second location spaced from the first location, the first location and the second location being selected to be such that, in use, there is a potential difference between the first position and the second position due to the current flowing in the structure; and

The collection module is arranged to collect electrical power from the current and supply electrical power to the downhole equipment.

According to yet another aspect of the present invention, there is provided a downhole power delivery system for powering downhole equipment in a well facility having a metal structure provided with cathodic protection, the system comprising:

A collection module as defined above electrically connected to the metal structure at two spaced-apart locations selected such that, in use, due to the flow of fluid in the structure cathodic protection current, so there is a potential difference between the two spaced-apart locations; and

The collection module is arranged to collect electrical power from the cathodic protection current and supply electrical power to the downhole equipment.

According to another aspect of the invention, there is provided a method of data communication in a well installation having a metal structure provided with a cathodic protection system such that there is an electrical circuit comprising the metal structure and a ground return due to the cathodic protection system, so current flows back around the ground, the method includes the following steps:

modulating the current at the first location to encode data; and

At a second location spaced from the first location, the effect of modulating the current at the first location is detected in order to extract the data.

One of the locations may be a location outside the wellbore, such as the surface, and the other of the locations may be downhole.

The step of modulating the current may include, among other things, and the modulating means may be arranged, among other things:

i) where the cathodic protection system is an external cathodic protection system, controlling the signal source of the external cathodic protection system to directly modulate the cathodic protection signal applied to the metal structure;

ii) modifying the connection between at least one anode and the metal structure so that at least one anode can for example be switched in or out of the metal structure, to modulate an electrical signal or to make the connection between the anode and the structure possible; impedance changes between ; or

iii) Changing the impedance of the circuit, which can be accomplished, for example, using variable impedance devices, or by switching components in and out of the circuit.

Techniques i) and ii) may only be available at one upper location, while technology iii) may be available downhole and at one upper location.

Communication using this general idea can be used for, for example, surface-to-downhole one-way communication, such as downhole-to-surface one-way communication, and two-way communication.

These techniques enable communication as part of a hybrid communication system, ie some parts of the signal channel are provided by modulating cathodic protection signals and some parts are provided by other techniques such as other wireless techniques including other EM techniques and acoustic techniques.

In each of the above cases, cathodic protection (where present) may be provided by a passive cathodic protection system or by an external cathodic protection system in which the sacrificial anode is connected to the well facility's Metal Structures, In an external cathodic protection system, a protective current is applied to the metal structure of the well facility.

In the present method and system, the aim is to utilise existing cathodic protection systems (or other current sources if available), in particular to utilise eg existing anodes in subsea installations (where they exist) without requiring to modify. Thus, the anode (where present) will typically be outside the wellbore (ie above the wellbore) and positioned in the water. Furthermore, the anode will typically be remote from the location where power and/or signal transmission is required.

Thus, any of the above systems may include one or more of: at least one existing anode; at least one anode disposed in water, such as a body of water in which a subsea well facility is disposed; remote to be achieved using the current generated by the anode At least one anode at the location of power and/or signal transmission.

Furthermore, any of the above systems may be arranged to enable transfer of power from the location where a current (eg, CP current) is applied to the structure to the collection location and/or the signal transmission location. This is true whether the current is passive CP current, imposed CP current, or other applied current. That is, typically, the source of the CP current or other current is remote from the collection location and/or the signal transmission location.

Furthermore, the metal structure can be uninterrupted in the region of at least one anode and/or in the region of the collection module.

In the case of optimization by modeling mentioned above, eg with regard to the spacing of the connections, the use of insulation, the choice of radial spacing or axial spacing only, and the selection of preset collection loads, the following parameters can be used in the model At least one of:

1. The decay rate at the top of the well derived from casing dimensions and tubing dimensions, weight and material type (resistivity) type, and resistivity of the overburden (medium surrounding the well).

2. The position of the upper connecting part.

3. The position of the lower connecting part.

4. The cross-sectional area and type of material (resistivity) of the upper cable used on the input of the collector.

5. Number, location, material (potential) and surface area of wellhead anodes.

6. The effective resistance of the well inspected from the seabed/wellhead, again derived from casing and pipe dimensions, weight and material type (resistivity) and resistivity of the overburden (medium surrounding the well) , but this time for all done.

In each of the above cases, the system may include a primary battery for supplying power independently of the collected power. The collection module may include the primary battery. In the case of a primary battery, the primary battery can be used preferentially while it maintains power. For example, it may be used to enable the use of higher data rates in the early stages, allowing the data rate to drop when only the collected power is available.

According to another aspect of the present invention, there is provided a well installation comprising a metal structure carrying electrical current and any of the above systems or instruments, such as at least one of the following: a downhole electrical energy harvesting instrument or system or a collection module; or a downhole well monitoring apparatus or system; or a downhole communication apparatus or system as defined above. Such a facility may also have a cathodic protection system for protecting the metal structure.

Note that, in general, each of the optional features that follow each of the above aspects of the invention is equally applicable to optional features of each of the other aspects of the invention, and may be Any necessary wording changes are rewritten after each aspect. For the sake of brevity, not all such optional features are rewritten after every aspect.

For example, it should be understood that any of the above-mentioned systems, methods, apparatus, and facilities may utilize collection modules, etc., having any combination or sub-combination of the above-defined features.

The wells mentioned in any of the above methods, systems, apparatus or facilities may be subsea wells.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 schematically illustrates a well facility including a well monitoring apparatus including a downhole power delivery system;

Figure 2A schematically illustrates a harvesting module of the power delivery system of Figure 1, and Figure 2B illustrates an alternative downhole unit;

2C is a schematic circuit diagram of a dc-dc converter that may be used in a collection module;

Figure 2D is a schematic circuit diagram of a dc-dc converter that may be used in a collection module;

3 schematically illustrates a well facility including a downhole communication apparatus including a downhole communication repeater and a downhole power delivery system for powering the downhole communication repeater;

4 schematically illustrates a well facility including a valve operating instrument including a remotely controlled downhole valve and a power delivery system for powering the remotely controlled downhole valve;

5 schematically illustrates a well facility including an alternative well monitoring system including a downhole gauge and a downhole power delivery system for powering the downhole gauge;

Figure 6 schematically shows an alternative well facility;

Figure 7 shows a graph of optimal collectable power versus depth of the lower connection for an arrangement of the type shown in Figure 1;

Figure 8 shows a flow diagram of energy harvesting optimization;

Figure 9 shows a flow chart of the operation of the downhole unit; and

Figure 10 schematically shows a well facility including a platform.

Figure 1 shows a well facility for an oil and/or gas well. As is well known, such oil and/or gas wells may be land wells or subsea wells (meaning wells located below any body of water), in which subsea wells the wellhead is submerged and on or on the seabed, riverbed, lakebed, etc. on the platform. Typically, well facilities are provided with cathodic protection systems. In the case of land wells, this cathodic protection system will most likely take the form of an impressed current cathodic protection system in which protective current is applied to the metal structure of the well. For subsea wells, on the other hand, the cathodic protection will most likely be a passive cathodic protection system in which multiple anodes of relatively reactive metals, such as magnesium alloys, are connected to the metal structure and exposed to the water in which the well facility is located.

Note that the present technology is also related to water injection wells, which are wells used in the art to inject water into a reservoir to aid in the production of oil and/or gas from other wells. Thus, a "well facility" in this specification may be a water injection well. Such wells would have a similar configuration to the facilities shown in more detail in this application. Similarly, the present technology can be used while drilling, as well as during production and after disposal. Thus, a well facility may be a partially completed facility in which drilling is being carried out. More generally, the present technology can be used during any period of the life cycle of the well facility.

Furthermore, while this detailed description is written with respect to installations in which cathodic protection is present, and this is particularly preferred, many of the systems and techniques of the present invention also function in other situations where electrical current flows over metallic structures flow and power can be harvested from the metal structure.

The well facility shown in Figure 1 comprises a wellhead 1 and a downhole metal structure 2 in a wellbore leading down from the surface S to the well. The well facility is provided with cathodic protection systems 3A, 3B. As mentioned above, this cathodic protection system would be an impressed current cathodic protection system 3A or a passive cathodic protection 3B comprising a plurality of anodes connected to the metal structure of the well facility (ie, connected to wellhead 1 or other metal parts connected to wellhead 1).

The downhole metal structure 2 includes a first length of metal tubing 21 extending down into the wellbore of the well, ie, production tubing. Surrounding this production tubing is a first casing 22 . Outside this layer is a second sleeve 23 and then a third sleeve 24 . As will be appreciated, there is a corresponding annulus between each length of metal tube. Thus, there is a first annulus between the production tubing 21 and the first casing 22, which is commonly referred to in the oil and gas industry as the "A" annulus, and is indicated by the reference numeral A in the drawings . Between the first casing 22 and the second casing 23 there is a second annulus, commonly referred to as the "B" annulus, and so indicated in the drawings, and in the second casing 23 There is a third annulus between and the third casing 24, which is commonly referred to as the "C" annulus and is so indicated in the figures. A well may also typically have another "D" annulus, and sometimes even more annuluses.

In other cases, the metal structure may include other elongated members, specifically, one or more of casing, liner, tubing, coiled tubing, sucker rod.

Monitoring equipment provided in the well facility includes an electrical power harvesting module 4, which in this embodiment is provided in the A-annulus. Collection module 4 is electrically connected to a pair of spaced-apart locations 41a, 41b on production tubing 21 via cable 41 . In an alternative, the collection module 4 may be electrically connected to one of the locations via a cable, but may be electrically connected to the other location without a cable. The collection module 4 may be electrically connected to one of the locations via the conductive housing of the collection module (or surrounding the collection module). Therefore, only one such cable would need to leave the housing.

Note that there is a galvanic connection between the collection module 4 and the metal structure 21 at the spaced locations 41a, 41b. In particular, there is a galvanic connection to the metal structure 21 rather than eg an inductive coupling. This simplifies construction and removes engineering difficulties. In the present case, there is always a galvanic connection from the metal structure to the input of the circuit included in the collection module for energy collection.

Furthermore, it should be noted that the metal structure of the well is generally not affected by the installation of this system. No insulating joints were introduced into any of the lengths of metal pipe to make the system effective, and the normal flow of cathodic protection current in the structure was not altered, other than, of course, the ongoing collection. Thus, for example, between the spaced locations, the segment of metal structure formed by the connection is continuous, and more generally, all segments of metal structure are continuous at these regions. This is not necessary for operation, but in a well facility it is possible and it is a normal general situation, ie the standard metal structure of the facility remains unchanged. Similarly, the current can and does flow in the same direction in the region of the connections and between the connections and in the metal structure. Again, this is a normal and common situation in well facilities, and modifications to the well facility are avoided. The current flow may be in a single segment of the metal structure formed by the junction, or jump from segment to segment or flow in parallel in several segments, it is critical that no manual arrangement of the metal structure in the well must be provided to allow the system to operate, and In this way, there is an uninterrupted current flow path provided by the metal structure, and the current flow is in the same longitudinal direction in the metal structure.

Note that the "A" annulus is generally accessible by wireline through the wellhead 1 . However, the use of the present arrangements is still advantageous because they minimize the number of penetrators in the wellhead, reduce risk and expense, and/or free up penetrators for other uses.

The monitoring apparatus also includes a downhole gauge 5 which is located deeper in the well than the collection module 4 and is connected to the collection module 4 via a cable 42 . In this embodiment, the downhole gauge 5 is positioned directly above the packer P. Typically, the cable 41 connecting the collection module 4 to the production unit 21 would be a Tubing Closed Conductor (TEC) as typically used in the oil and gas industry, and the cable 42 connecting the collection module 4 to the downhole gauge 5 would also be Tubing Enclosed Conductor (TEC). Furthermore, typically the cross-sectional area of the conductors in the multi-segment cable 41 connecting the collection module 4 to the production tubing 21 will have a larger cross-sectional area than the cross-sectional area of the cable 42 connecting the collection module 4 to the downhole gauge 5 cross-sectional area of .

In the case where cathodic protection is provided in a well facility, the potential of the metal structure of the well takes a sufficiently negative potential at the injection point (eg, wellhead 1 ) so that when the downhole metal structure 2 descends into the well, the potential at the wellhead and along the Corrosion at other points of the downhole metal structure 2. However, the magnitude of this negative potential decreases as the downhole metal structure progresses further down the well due to losses in the system. Therefore, the potential of the metal structure 2 will be more negative near the wellhead than at a deeper position in the well. Therefore, when cathodic protection current is flowing in the well facility, there will be a potential difference between location 41a and location 41b where the first of the cables 41 is connected from the collection module to the production tubing 21, at location 41b Here, another of the cables 41 is connected from the collection module 4 to the production tubing 21 . Therefore, the collection module 4 will see the potential difference across it and in this way energy can be extracted from the cathodic protection current.

It should be noted that extracting energy will use power from the cathodic protection system, however the effect on the effectiveness of the cathodic protection system or any acceleration of corrosion of the anode will be negligible. Typically, the cathodic protection current will be about 10 amps, while the present system can draw, for example, 10-100 mA. Therefore, the amount of current drawn is well within the tolerances normally allowed when developing cathodic protection systems. If desired, increased levels of impressed current can be provided, or the number of anodes provided can be increased beyond the norm. This will increase the cathodic protection current, thereby improving collection.

Electrical power can be collected from the system at the downhole location of the collection module 4, and this collected power can be used for other purposes.

In the arrangement of Figure 1, this collected power is used to power downhole gauges 5 and allow readings to be taken from downhole gauges 5 and communicated to the surface S.

In this embodiment, the upper communication unit 6 is arranged to communicate with the collection module 4 and the downhole gauge 5 . In this case, the upper communication unit 6 is arranged at the ground S (in this case, the land ground).

It will be appreciated that arrangements such as the present arrangement can be used in place of conventionally installed permanent downhole gauges (PDGs), with the advantage that the use of penetrators through the wellhead can be avoided, while the longevity of well monitoring will be feasible in many cases of. Monitoring may be monitoring of reservoir pressure or similar monitoring of pressure in a closed annulus, if desired, to, for example, help detect any leaks, problems or failures in the system. In such a case, the sensor and collection modules may be positioned in a closed annulus.

All of these options are possible, for example, in subsea well installations, where there will normally be a current to be collected (ie, CP current, typically generated by sacrificial anodes positioned in the water in which the subsea installation is provided) ), and other power options and signaling options are more problematic in subsea well installations.

In wells with subsea wellheads, it is conventionally not possible (practically/cost effective) to provide hydraulic or electrical connections to the outer annulus (B, C, etc.). Especially where the annuluses are sealed at their bases, it is useful to monitor and optionally control the pressure in these annuluses, eg, to reduce the risk of high pressure causing casing collapse. In particular, flow or well drilling can increase the temperature of the sealed outer annulus, thereby increasing the pressure in said outer annulus. The ability to monitor and optionally control pressure in such situations, such as with a vent valve between the annuluses, as mentioned elsewhere, would be beneficial. In particular, monitoring the pressure in the closed annulus would permit production at a higher rate than would be achievable using the modeling of the expected pressure rise alone, since the use of the modeled pressure would require greater A safety margin and potentially a correspondingly reduced production rate. As should be appreciated, the present technology may facilitate such monitoring and/or control.

Another specific embodiment of the present technology would include a sensor module positioned at the same location and for the same purpose as is most common with conventional permanent downhole gauges And set.

Thus, a sensor module may be arranged in the A-annulus and arranged for monitoring the reservoir pressure by sensing the pressure in the tubing via a pressure communication port through the tubing, allowing for inference of the reservoir based on the sensed pressure Laminar pressure, taking into account static pressure and flow effects. As is the case with conventionally used PDGs, reservoir pressure will generally be inferred rather than measured directly in this manner (locating sensors directly in the reservoir is often not feasible), as should also be understood, "monitoring reservoir pressure" Covers the use of such measurement techniques.

The collection module can also be arranged at the location of the sensor module.

Different techniques can be used to allow data to be extracted from the downhole gauge 5 towards the surface.

In this embodiment, the collection module 4 is arranged to accept a signal from a downhole gauge indicative of the parameter to be measured, eg pressure and/or temperature, and by modulating the collection module 4 at spaced connections 41a and 41b to transmit this data towards the ground. In turn, this load change changes the amount of current drawn from the cathodic protection current applied to the system. This in turn is detectable at ground or other convenient location due to changes in the electrical potential of the metal structure at ground or other convenient location. It can be detected eg by detecting a change in potential at the wellhead 1 or by detecting the voltage across the power supply used in the external cathodic protection system 3A or the current checked by the power supply used in the external cathodic protection system 3A. In this embodiment, the effect of this modulation is detected by the upper communication unit 6 monitoring the potential of the wellhead relative to a reference ground to extract pressure and/or temperature measurement data.

Preferably, the separation between the spaced apart connections 41a, 41b is at least 100 meters, and more likely in the range of 300 to 500 meters. The optimal spacing for the spaced connections 41a, 41b can be determined by modeling a given facility. As the distance between these connections increases, this tends to increase the potential difference between the connections (although the rate of increase of the potential difference decreases as the depth of the lower connections increases). On the other hand, as the interval increases, the total length of the cable 41 and thus the resistance of the cable 41 increases. Therefore, in most systems, there will be an optimal interval.

Figure 2A shows the collection module 4 of the instrument shown in Figure 1 in more detail. In this embodiment, the collection module 4 has a pair of terminals 43a, 43b to which the respective cables 41 are connected. There is a galvanic connection between the metal structure and the terminals 43a, 43b. Connected between these terminals 43a, 43b is a low voltage dc-dc converter for collecting electrical energy in the presence of a potential difference across the terminals 43a, 43b. The dc-dc converter 44 is connected to a charge storage device 45 which includes at least one low leakage capacitor and is connected to and controlled by a microprocessor driven central unit 46 . The charge storage device 45 and the central unit 46 are also connected to the length of cable 42 leading to the downhole gauge 5 via respective terminals 43c. In an alternative, the charge storage device 45 may be omitted, ie sufficient power may be collected on or on demand to allow continuous operation.

In operation, the central unit 46 controls the operation of the dc-dc converter 44 in order to optimize the load (which is presented to the current by the collection module 4 due to the cathodic protection current) to maximize what can be collected and used or used Energy stored in charge storage device 45 . Note that the central unit may be arranged to directly selectively use and/or deliver harvested energy where appropriate, and to store and extract stored energy where appropriate.

Note that in one alternative, the microprocessor driven central unit 46 may be replaced by alternative electronics including, for example, analog feedback circuits or state machines or even based on fixed harvesting loads modeled for a particular facility.

When the stored energy is to be used, the power from the charge storage device 45 is fed to the downhole meter 5 via the cable 42 and the readings from the downhole meter 5 are taken by the central unit 46 via the cable 42 . The central unit 46 also controls the operation of the dc-dc converter 44 to modulate the load introduced between terminals 43a and 43b to send a signal back to the surface carrying the reading from the downhole gauge 5, as described above.

Note that in this embodiment, the dc-dc converter 44 and the central unit 46 together act as a variable impedance since the central unit 46 controls the operation of the dc-dc converter 44 to introduce a variable impedance between the terminals 43a and 43b device.

Note that, in the alternative, the appropriate sensors may be provided at the same location as the collection module 4, rather than in a separate downhole gauge 5.

In particular, a downhole unit 4a as shown in Fig. 2B may be provided, which comprises both the collection module 4 and at least one downhole device to be powered. In this case, the downhole unit 4a includes a pressure sensor 47 and a communication unit 48 .

In such a case, there may be no secondary cable 42 leading away from the downhole unit 4a. On the other hand, in some other cases, downhole unit 4a may still be used to power external equipment, even including its own sensors 47 and/or communication unit 48, so that secondary cables 42 may be present.

In the alternative, the downhole unit 4a may use its own communication unit 48 for communicating back towards the surface, rather than using load modulation techniques as described above to communicate with the surface. Such communication may be in the form of EM communication signals that may be applied back to the downhole metal structure 21 via the cable 41 . In other cases, the communication unit 48 provided in the downhole unit 4a may be an acoustic communication unit for applying an acoustic signal to the metal structure 21 for transmission back towards the surface. In such a case, the upper communication unit would then be arranged to receive acoustic signals. It will be appreciated that bidirectional communication may be provided throughout any or all portions of the communication channel as desired or when desired. The other two communication techniques can be used in parallel in either branch of the communication channel, so EM signals and acoustic signals can be used side-by-side.

In further alternatives, the collection module 4 or downhole unit 4a may include at least one power converter for controlling the voltage of the collection power for delivery to the charge storage device 45 and/or other components such as the central unit 46 . It may be desirable to store energy at a different voltage than when the energy was harvested and/or at a different voltage than when the central unit 46 or other components use the energy. For example, it may be desirable to store power at a higher voltage than the voltage at which the power is collected and/or consumed. This may be useful, for example, if there is a large draw on stored power, such as during transmission.

One possible implementation for a dc-dc converter is to use a commercially available integrated circuit. An alternative is to create a similar circuit using discrete components. In order to provide efficient performance, it is desirable to have a dc-dc converter capable of handling low input voltages. One way to achieve this is to use field effect transistors, such as JFET switches, to form a resonant boost oscillator using a boost transformer and coupling capacitors. To help optimize energy harvesting, the turns ratio on the transformer can be selected, preferably dynamically during operation. Multiple taps may be provided on the secondary of the transformer, which may be selectively used to provide corresponding turns ratios.

A processor, such as that of the central unit, may be arranged to control the switches to dynamically select the corresponding taps and thereby control the load generated by the dc-dc converter.

Figure 2C shows a schematic circuit diagram of one possible implementation for a resonant boost oscillator of the type described above. The available input potential difference can be connected across the input terminal as Vin and there is an output Vout across the output terminal. The circuit includes a field effect transistor 201 , a boost transformer 202 and a rectified output arrangement 203 which together act as an oscillator, the rectified output arrangement 203 including a crossover diode pair 206 and a corresponding coupling capacitor 205 . The primary winding 202a of the transformer 202 is connected in series with the FET 201, and the input Vin is applied across these. The gate of the FET 201 is connected to the secondary winding 202b of the transformer 202 . There is an output Vout across coupling capacitors 205 which are each connected across the secondary winding 202b via respective diodes 204 .

The secondary winding 202b of the transformer 202 includes a plurality of taps 202c that can be selected using a switch 206, allowing the turns ratio to be adjusted. The switch 206 may be controlled by a microprocessor, in this case the central unit 4b.

This type of dc-dc converter arrangement can function even when the potential difference (input voltage) present across the terminals is low (ie 0.5V or less). In practical embodiments, this input voltage may be less than 0.25V and possibly even less than 0.05V. Since this is very low compared to the semiconductor bandgap voltage (eg, 0.7V), many types of dc-dc converters will not function, allowing energy harvesting at such input voltages. However, dc-dc converters based on the above principles can function at even such low voltages. Such dc-dc converters may be considered to include start-up means arranged to allow operation at higher voltages when the input voltage is 0.5V or below.

An alternative is to provide a circuit with a discrete power source that acts as part of the starter. Thus, for example, a battery can be provided once to start the system after installation. Furthermore, the energy stored in the energy storage can be used to restart the system if energy harvesting is temporarily stopped.

Figure 2D shows a schematic circuit diagram of one possible implementation of a dc-dc converter operating on such a basis. The dc-dc converter of Figure 2D includes an H-bridge 207 of transistors 207a across which the input voltage is connected. The gate of transistor 207a is connected to a control unit 208 arranged to control the switching of transistor 207a to generate the ac output. The ac output of the H-bridge 207 is connected across the primary winding 202a of the step-up transformer 202. The secondary winding 202b of the transformer 202 is connected to the rectifier 209 . One output of the rectifier 209 is connected to the input of the power supply unit 210 via the diode 204, and the other output is connected to ground. Also connected to the input of the power supply unit 210 via another diode 204 is a battery 211 .

A power supply unit 210 is arranged to supply power to the control unit 208 . To start the operation, the power supply unit 210 may use power from the battery 211 . When energy is being collected through the dc-dc converter, then the power supply unit 210 may use the power received from the rectifier 209, ie the collected power.

Although in this embodiment the power is used directly as it is harvested, in the alternative, the harvested energy can also be stored in and used from a storage device. As described elsewhere in this application, the storage device may, for example, include at least one low leakage capacitor and/or at least one rechargeable battery. With energy stored, this allows the mechanism to restart the system if collection stops at any point after the battery 211 has been discharged.

The battery 211 may be a primary (disposable) battery, or may be a rechargeable battery, as long as it is charged when installed. Where the battery is a rechargeable battery, in some embodiments the power supply unit 210 may be arranged to store energy therein when available, alternatively it may be more convenient to provide a separate energy storage device (the The energy storage device may include a rechargeable battery).

Note also that, in another alternative, a dc-dc converter of the type shown in Figure 2D may be arranged to allow control of the load generated by the dc-dc converter. Thus, for example, an arrangement similar to that shown in Figure 2C could be used, where the secondary winding 202b has multiple taps and a switch is provided to allow selection of the taps. This switch may be located between the windings and the input of the rectifier 209 . In another alternative, discrete secondary windings can be provided instead of multiple taps to achieve similar results. As in the case of the arrangement of Figure 2C, the switch may be controlled by the control unit.

Note also that in other embodiments, the collection module 4 and downhole gauge 5 (or downhole unit 4a) may be positioned in other annuluses within the well facility than in the A-annulus. Furthermore, the gauge may be arranged to sense parameters in a different annulus than the annulus in which it is located.

For example, these components may be arranged in either the B annulus or the C annulus, and a gauge positioned eg in the B annulus may be arranged to sense one of the A annulus, the B annulus, the C annulus, or any combination thereof or multiple parameters. It should be noted that these are locations where attempting to provide direct cable connections from the ground is generally not possible or at least undesirable. Thus, the techniques of the present invention create the possibility to monitor the pressure in, for example, the B annulus or the C annulus, over the lifetime of the well facility, where using conventional power delivery methods would be difficult and/or expensive. The techniques of the present invention avoid the use of penetrators through the wellhead, which can reduce risk and cost. They also offer relatively simple, neat, and easy-to-install solutions.

Figure 3 shows a well installation similar to that of Figure 1 but including a downhole communication repeater 7 instead of a downhole gauge. The repeater 7 is arranged in the B-ring together with a collection module 4 of the same type described above with respect to Figs. 1, 2A to 2D. Here again, the collection module 4 collects power from the cathodic protection current in the metal structure 2 and provides this power to the downhole communication repeater 7 .

The structure and operation of the well facility, cathodic protection system and power delivery system in the arrangement of Figure 3 are substantially the same as in the system described with reference to Figures 1, 2A-2D. The only difference is that the downhole component delivering power through the power delivery system is the communication repeater 7 instead of the downhole meter 5 .

Therefore, for the sake of brevity, a detailed description of the well facility and power delivery system is omitted here. Where the same components are referred to in relation to this embodiment as in Figures 1 and 2A-2D, the same reference numerals are used.

Downhole communication repeaters 7 are arranged to pick up signals from the downhole metal structure 2 in the area of the repeaters 7 and transmit the relevant data onwards towards the surface. In this embodiment, the signal is applied to the downhole metal structure 2 as an EM signal by a transmission tool 71 positioned further down the well (eg, in the production tubing 21). Correspondingly, the repeater 7 is arranged to pick up the EM signal.

In the alternative, different types of transmission means may be arranged to transmit the signal picked up by the transponder. Such a tool may for example be arranged outside the oil pipe.

In the alternative, the communication repeater 7 may be arranged to pick up from the downhole metal structure 2 an acoustic signal that has been applied further downhole.

Similarly, the downhole communication repeater 7 may be arranged to apply acoustic signals to the downhole structure 2 for transmission towards the surface, or may be arranged to apply EM signals to the downhole metal structure 2 for transmission to the surface, Or may be arranged to utilize the impedance modulated signal transmission techniques described above.

Thus, for example, the communication repeater 7 may pick up signals at its location and transmit these signals along the cable 42 by applying the signals to the collection module 4 or by modulating the load it places on the power supply in the collection module 4 to collection module 4. Similarly, the collection module 4 may be arranged to apply a signal to the metal structure 2 for transmission towards the ground, or may be arranged to modulate the load it generates between the spaced connections 41a, 41b for use in For detection at the ground by the upper communication unit 6 .

Note that where a downhole communication repeater 7 is provided, the EM signal may be picked up and/or applied, for example, by the repeater 7 using spaced contacts or using inductive couplings or the like, the spaced contacts being formed to A metallic structure, the inductive coupling comprising a toroid or signal transmission across an insulating joint (if there is one). Similarly, conventional acoustic signal pickup and application techniques can be used.

In the alternative, there may be communication from the surface down to the downhole location, and typically bi-directional communication. Thus, the repeater 7 can act as a repeater in both directions. Again, the two communication techniques can be used in parallel on at least one branch of the channel to provide redundancy.

Note also that the downhole communication repeater 7 may be provided in a location so as not to be in the product flow while allowing the life of the well operation.

Two specific embodiments related to Figure 3 are:

1. The repeater 7 includes a continuously powered EM receiver located at a depth of 3m-500m that receives and decodes messages or retransmits the original data/signal continuously at higher frequencies using only load impedance modulation , for decoding at the ground.

2. The transponder 7 comprises a continuously powered acoustic receiver located at a depth of 3m-500m which receives and decodes the message and then retransmits the data to the surface using load impedance modulation.

Note that in both cases, the transponder 7 may be provided in the downhole unit together with the collection module, or may be separate from the collection module. Again, the repeater can also be a two-way repeater.

In any of the systems described in this specification, the device may be arranged to manage the power budget by using intermittent operation of components such as EM or acoustic receivers and/or transmitters, ie using less energy overall.

Figure 4 schematically illustrates a well facility comprising remotely controlled valves and a power delivery system of the same general type as described above.

The general structure and operation of the well facility and the power delivery system are again generally the same as those described above with respect to the arrangements shown in FIGS. 1 , 2A-2D . Therefore, for the sake of brevity, a detailed description of these common elements is omitted here, and the same reference numerals are used to designate those features that are common between the two embodiments.

In this embodiment, the well facility includes a first hydraulically operated subterranean safety valve SSSV as conventionally placed in production tubing 21 .

Here, however, an additional underground safety valve 8 is also provided within the production tubing 21, but further down the well. Therefore, in the present case, a second underground safety valve 8 is provided as an additional safety measure or fallback measure. However, in the alternative, the hydraulically operated underground safety valve SSSV may be omitted.

The second underground safety valve 8 is powered and operated by utilizing a power delivery system. In particular, the collection module 4 is connected to the second underground safety valve 8 via a cable 42 and is arranged to issue power and control signals to the second underground safety valve 8 via the cable 42 . Thus, energy is harvested from the cathodic protection current traveling in the downhole structure 2 and this energy is used to control and operate the second subterranean safety valve 8 .

Such a subterranean safety valve 8 can be positioned deeper in the well than a conventional hydraulically operated subterranean safety valve SSSV. This is because it is not subject to the same range limitations as hydraulic drive systems, requiring no hydraulic fluid to be driven towards it. It should be noted that here the control signal for the second underground safety valve 8 may be transmitted by the upper communication unit 6 via the metal structure of the wells 1 , 2 to be detected by the collection module 4 and forwarded to the underground safety valve 8 . In some cases, valve 8 may be made to operate in a fail-safe mode, whereby the valve will close in the absence of power and/or control signals. Note that in an alternative, of course, the valve 8 and collection module may be provided as part of a common downhole tool 4a. Additionally, in some cases, the power used to close the valve may come from another source, where the downhole power delivery system supplies power for controlling the operation and/or operating the trigger mechanism.

Figure 5 shows an alternative well facility including a well monitoring instrument. Here, again, there are similarities to the arrangements shown and described with reference to Figures 1, 2A-2D. Again, there are collection modules 4 disposed within the downhole metal structure 2 and connected to spaced locations on the downhole structure 2 and, in addition, there are downhole gauges 5 connected to the collection modules 4 . In this case, both the collection module 4 and the downhole gauge 5 are positioned in the B annulus to provide monitoring of the conditions in this annulus. The downhole gauge 5 may, for example, include pressure sensors and/or temperature sensors.

In this case, the spaced-apart locations 41a, 41b are provided on different sections of the downhole metal structure 2 . In this embodiment in particular, a first connecting portion 41 a of the connecting portions is formed to the second sleeve 23 and another connecting portion 41 b of the connecting portions is formed to the first sleeve 22 . The system works on a similar principle as discussed above and therefore relies on the potential difference existing between the two connections 41a, 41b. In the present embodiment, this potential difference is achieved by insulating the two sections of metal structures 22, 23 from each other at least in the region of these connections. This means that for the cathodic protection current from the two segments of metal structure 22 , 23 there are different paths to ground. In this embodiment, the means for insulating the two sections of metal structures 22, 23 from each other includes an insulating coating 91 provided on the outer surface of the first bushing 22 and an insulating coating 91 provided on the first bushing 22 to hold the first bushing A plurality of insulating centralizers 92 separate from the second sleeve 23 .

Preferably, this insulation 91 and the centralizers 92 will be provided over a length of the first sleeve 22 of at least 100 meters and more likely 300 to 500 meters. Where desired and practical, insulating spacers may be mounted on the metal structures forming the outer segments of the annulus. Thus, for example, it is mounted on the second sleeve 23 in the above embodiment. Note that the insulation need not be completely continuous to provide a useful effect. Generating different paths to the ground is the purpose. Thus, while for example the insulation may be provided over 100 meters, it may not be continuous, or continuous insulation may be provided over this distance.

The benefit of the arrangement shown in FIG. 5 is that the long length of cable 41 between the collection module 4 and the metal structure 2 required in the arrangement shown in FIG. 1 can be omitted. This means that the system can be easier to install. For example, the system can be deployed with the housing of the collection module 4 mounted on a piece of metal pipe and provided with sliding contacts across the annulus to contact another piece of pipe. To further simplify the location, the downhole gauge 5 can be omitted and the sensor provided with the collection module 4 in the downhole unit 4a. Such an arrangement can reduce the rig time required for installation.

Therefore, in some cases, it may be preferable to provide insulating means 91 , 92 over the provision of cable 41 . Which system is preferred for a given facility can be determined by external factors related to the facility or possibly by modeling a particular facility.

However, in typical situations where it is feasible to use the system, the arrangement of Figure 1 may give better performance than the arrangement of Figure 5 .

In an arrangement of the type shown in Figure 5, it is possible to detect relatively high currents but relatively low potential differences through the collection module. Thus, in the arrangement of Figure 5, the potential difference may be, for example, 10mV-20mV, and the current may be, for example, 1A. On the other hand, in the arrangement of Figure 1, the potential difference may be, for example, 100 mV-200 mV, and the current may be, for example, 100 mA-150 mA. The higher potential difference is achieved by the larger spacing given by the cables 41 in the arrangement of Figure 1, but the lower current is caused by the resistance of the cables.

Apart from this difference in how the connections are formed and the potential difference is achieved, and the different advantages and disadvantages that come with it, the structure and operation of the system as shown in FIG. 5 is similar to that shown in FIG. 1 . Therefore, the different alternatives explained above with respect to FIGS. 1 to 4 also apply in the case of using a system such as that shown in FIG. 5 .

That is, the insulation and connection arrangement shown in Figure 5 may be used in each of the embodiments shown in Figures 1 , 3 and 4, and similarly, the different discussed above The collection module 4 and downhole unit 4a of the form may be used in an arrangement such as that shown in FIG. 5 .

Note that in some cases it may be desirable to use the present power delivery system to provide a ready wireless well facility even though the wireless functionality was not intended to be used when the well was first installed.

Thus, when the well is first installed to make it wireless ready, the arrangement shown in Figure 3 can be set up, wherein the communication repeater 7 and associated power delivery system are included in the B-ring. This will facilitate communication with the surface if a decision is made to use it at a later time, eg, the downhole wireless signalling tool 71 sending a signal to the surface. Here, again, note that we mean "wireless" between downhole and outside, i.e. no cables/wires pass through the wellhead.

In other cases, the system can be retrofitted. For example, a system such as that shown in Figure 1 installed in the A-annulus may be retrofitted when the production tubing is replaced. In another case, the system may be installed in the main bore of the production tubing. It is important to note that each of the arrangements and techniques described in this specification avoids the need for a cable to penetrate the wellhead 1 . Therefore, these systems can be used without a penetrator available or when the use of a penetrator is objectionable.

While the arrangement in Figure 4 shows the provision of an additional underground relief valve 8, in other cases a different type of (possibly remotely operated) valve or component could be provided. For example, an arrangement of the type shown in Figure 4 can be used with annulus vent valves provided in wells to allow controlled flow between one annulus and another or between annulus and a bore Fluid communication or exhaust. The valve may include a gas lift valve for allowing gas from the A-annulus to enter the bore of the production tubing. Similarly, the valve may be a packer, through-packer valve, or packer bypass valve. Again, used to allow a specific annulus to be vented from the ground in a controlled manner. In another embodiment, the valve may include a flow control valve to control the contribution from a zone, or provide a means to achieve improved pressure buildup data capture by eliminating the effects of wellbore storage. Note that in each case the valve could be a flow control device that would not allow complete shut-off of flow, but act as a variable choke, for example.

In each case, the valve or component may be a wirelessly controlled valve or component.

In another alternative, the present technology may be used to communicate with, and/or control communication with, a tool supported by wireline/skid wire or attached to coiled tubing in production tubing 21 A tool that supports or attaches to coiled tubing in production tubing 21 . That is, such a tool may be arranged to apply a signal to and/or pick up a signal from the oil pipe, the signal being passed through the repeater 7 .

With this type of system, one might be able to extract power at a level of perhaps 50mW. Therefore, the amount of power that can be extracted is not particularly large, but the fact of interest is that this power can be available throughout the life of the well and is sufficient to perform useful functions such as controlling downhole equipment, taking important measurements and allowing the These measurements are transmitted to the ground).

Note that generally in embodiments of the general type shown in Figures 1-4, the collection efficiency will be dominated by the cross-sectional area of the cable 41 and the source impedance provided by the connections 41a and 41b is low. This means that there is little degradation in the performance of any one collection module 4 if multiple collection systems are included in a well facility. Note that generally any additional collection system will have its own cable 41 where appropriate. This is based on losses in the cable meaning that by having more than one collection system share a cable, usually very little loss will be gained.

Typically, multiple collection modules of any of the types described above may be provided in a well facility. Thus, for example, gauges can be set to monitor conditions in the production tubing, gauges can be set to monitor the annulus, and valves can be set, all with power supplied from separate respective collection modules. Similarly, any one collection module can be used to power multiple devices. In some cases, each device may have a dedicated cable from the collection module. In other cases, there may be multi-drop systems where one cable from the collection module is used to connect to multiple downhole equipment. The manifold system may be arranged to allow power delivery and communication with multiple downhole devices. In this way, the cable can carry power signals, communication data and addressing data. Correspondingly, the collection module may be arranged to manage the multidrop system.

Note that while in the above embodiments the cables 41, 42 run within an unobstructed annulus, in other cases one or more of the cables 41, 42 may pass through a packer (including an intumescent seal) spacer), cement or other annular sealing device.

It should also be understood that, in at least some instances, features of the present system and apparatus may have a distributed form. Thus, for example, the collection module may be provided in a plurality of discrete parts, components or sub-modules that may be positioned differently.

Fig. 6 shows an alternative well facility that has similarities to the facility shown in Fig. 1 and the same reference numerals are used to designate features common to the embodiment of Fig. 1 and are omitted A detailed description of these common features.

The well facility shown in FIG. 6 helps illustrate in greater detail some of the alternatives described above with respect to each of the well facilities shown and described with reference to FIGS. 1-5 .

The well facility includes monitoring equipment in the same manner as in FIG. 1 . Thus, there is a collection module 4 connected via a cable 41 to a pair of spaced apart locations 41a and 41b. In this case, however, the first of the positions 41a is located on the production tubing 21 so that the first of the cables 41 is connected to the production tubing, while the second of the spaced positions 41b is located on the production tubing 21 on the casing 22. Thus, in this embodiment, there is an axial and radial separation between the connections 41a, 41b so that the collection modules 4 are connected across the "A" annulus. Furthermore, insulating portions 91 are provided on the production tubing 21 and in the region of the second connection portion 41b, extending axially on either side of this production tubing. Note that in another alternative, a connection may be to the formation rather than to the metal structure. In some cases, all of the instruments of the power delivery system may be positioned outside the casing, ie, between the casing and the formation. This is generally not desired from a risk/difficulty point of view when installing, but it is possible.

Furthermore, in this embodiment, there are a second collection module 4' and a third collection module 4" disposed in the "A" annulus (which are part of the respective downhole units). In this embodiment, these other collections Each of the collection modules 4', 4" utilizes the same first cable 41, and as such, one terminal of each of the collection modules 4', 4" is connected to the first connection point 41a. Note that, In other embodiments, separate cables may be used to form these connections to the first connection point, and this would be preferred, resulting in improved performance. A single upper cable (as shown) is possible though , is unlikely to be used, but helps to simplify the drawing. In some cases, multiple collection modules may be provided that are distributed across different annuluses.

In this embodiment, similar to the embodiment shown in FIG. 1 , the first collection module 4 is connected to the downhole gauge 5 via a secondary cable 42 . Here, however, the downhole gauge 5 is positioned below the packer P and the cable 42 is passed through the packer P. In this case, the gauge 5 is arranged for pressure and/or temperature measurement of the conditions inside the production tubing 21 through ports 21a provided in the wall of the production tubing 21 . That is, although the downhole gauge 5 is positioned in the "A" annulus, it is arranged to measure parameters within the production tubing 21 .

Furthermore, in this embodiment, a second downhole gauge 5' and a third downhole gauge 5" are provided. In this embodiment, each of the downhole gauges 5, 5', 5" is via the same A secondary cable 42 is then connected to the collection module 4 . Thus, this is a multidrop system and cables 42 are used to carry power signals, control signals, parameter data and addressing data to allow powering and extraction from each of the meters 5, 5', 5" reading.

Note that in alternative embodiments, many downhole gauges or other downhole equipment may be powered from one collection module 4 via individual dedicated cables 42 rather than a single cable as in this embodiment. Furthermore, as mentioned above, while in this embodiment there are multiple gauges extending from one collection module, in other embodiments one collection module may be used to power different types of downhole equipment . Thus, a collection module can be used, for example, to power downhole gauges, downhole repeaters and downhole valves.

In this embodiment, the second collection module 4' is part of a downhole tool that includes the collection module and the sensor. In the present case, the sensor is arranged to measure parameters in the "B" annulus via a port 22a provided in the first sleeve 22 . Thus, for example, sensors in the second collection module 4' may be arranged to measure pressure and/or temperature in the "B" annulus.

Furthermore, in this embodiment, the third collection module 4" is again part of a downhole tool, which in this case comprises a collection module and sensors for interfacing with sensors disposed in the "B" annulus and the "C" annulus 605 is a communication unit for communication. Here, the communication between the sensor 605 and the second collection module 4" is carried out via wireless means. Thus, for example, there may be inductive signal transmission or acoustic signal transmission between the sensor 605 and the collection module 4". The sensor 605 may be placed as physically close to the collection module 4" as possible.

It will be appreciated that once the data is at the upper communication unit 6, it can be transmitted onward to any desired location, to the desktop location D, for further processing using standard communication technology (such as mobile communication technology, the Internet, etc.) and/or consult. Of course, a wired connection can also be provided between the desk position and the upper communication unit 6 .

In addition, data can also be sent from the tabletop position D to the upper communication unit 6 for transmission downhole. Thus, for example, control signals may be transmitted downhole from tabletop position D via upper communication unit 6 to control the operation of collection modules or sensors or downhole valves or repeaters, etc., and similarly, any desired transmission may be sent downhole in this manner The data.

In another alternative, the insulation may be provided on the exterior of the outermost casing (eg, in the embodiment shown in FIG. 6 , the third casing 24 ) and in an area adjacent to the wellhead 1 . This can help drive the maximum negative potential caused by the cathodic protection current further down into the well. This is due to minimizing leakage in this area near the wellhead. Thus, providing insulation on the outermost casing may help to allow the uppermost connection 41a to be positioned lower in the well without significantly reducing the effectiveness of the system. If one considers the potential decay curve, by providing insulation on the outermost casing 24, the negative potential will decay very slowly in the insulated area near the wellhead, and then start to decay more rapidly once it reaches the non-insulated area.

Figure 7 is a graph showing one embodiment of how the optimum power available for harvesting in a well facility varies with depth in the well. As mentioned above, due to the increase in the potential difference available due to the increased spacing between the connections on the one hand and the resistance of the cable on the other hand, there tends to be an optimum depth of the lower connection 41b, or in other words In other words, there tends to be an optimum interval between the two connecting portions 41a and 41b. The graph shown in Figure 7 relates to the position of the upper connection 41a approximately 5 meters below the wellhead and thus in the area of the liner hanger. In this embodiment, it can be seen that the optimum depth of the lower connector is approximately 550 meters down the well. However, it can also be seen that a considerable proportion of the optimum power can be collected at depths between, for example, 300 meters and 950 meters. In general, it would be desirable to minimize the length of the cable while achieving optimal power harvesting, which implies minimizing the depth of the second connection. However, there may be situations in which it is possible to take advantage of the fact that the collection module can be placed deeper in the well.

The optimal location for the upper connection may depend on where the CP current (or other current) is injected and where the current or the potential caused by the current is maximized. The present method and system may include the steps of first determining the location where the applied current (or potential) has a maximum magnitude, and selecting the location of the upper connection portion accordingly.

Where the well is a land well, the upper connection may be within 100 meters, preferably within 50 meters of the surface.

Where the well is a subsea well, the upper connection may be within 100 meters, preferably within 50 meters of the mudline.

As mentioned above, although the above description refers to current collection from cathodic protection and this is preferred, if other currents are present in the metal structure, they may equally be used.

It will be appreciated that although specific examples are given above, in general any of the components of the system may be positioned in any available annulus.

In cases where it is mentioned above that, for example, with regard to the spacing of the connections, the use of insulation, the choice of radial spacing or axial spacing only, and the selection of preset collection loads to be optimized by modeling, the following parameters can be used in the model At least one of:

1. The decay rate at the top of the well derived from casing and tubing dimensions, weight and material type (resistivity) type and resistivity of the overburden (medium surrounding the well).

2. The position of the upper connecting part.

3. The position of the lower connecting part.

4. The cross-sectional area and type of material (resistivity) of the upper cable used on the input of the collector.

5. Number, location, material (potential) and surface area of wellhead anodes.

6. The effective resistance of the well as seen from the seabed/wellhead, again derived from casing and pipe dimensions, weight and material type (resistivity) and resistivity of the overburden (medium around the well) Yes, but this time for all done.

In particular embodiments of the above systems, the one or more cables 41 used in connecting the collection module to the structure/surroundings may have a cross-sectional area of, for example, 10 mm ² to 140 mm ² . ^10mm2 may be considered the low end of the desired operating cable size. Normally, a larger cross-sectional area will be preferred. The 140mm ² cable may be a Kerite (RTM) LTF3 flat type cable. This represents the upper end of the cables currently available on the market, however, larger sizes can be used if available.

FIG. 8 is a flow diagram illustrating a process for optimizing energy harvesting of a harvesting module of the type described above.

In step 801 , the dc-dc converter 44 starts up using the initial settings/configuration and delivers available energy to the charge storage device 45 .

In step 802, it is determined whether sufficient voltage is present to power the microprocessor in the central unit 46. If no, this step 802 is repeated until the answer is yes, and when the answer is yes, the process proceeds to step 803 where the microprocessor in the central unit 46 is powered.

Then, in step 804, the microprocessor measures the power output from the energy harvester, and in step 805, the microprocessor modifies the dc-dc converter 44 settings to slightly increase the load. Then, in step 806, it is determined whether this results in an increase in collector output. If the answer is yes, the process returns to before step 805 so that the dc-dc converter 44 settings can be changed again to slightly increase the load.

On the other hand, if it is determined in step 806 that the output is not increasing, the process proceeds to step 807 where the microprocessor modifies the dc-dc converter 44 settings to reduce the load slightly and the process returns to step 807 806, so it can be determined if this is causing the output to increase.

After this, steps 805 , 806 and 807 are iteratively repeated during energy harvesting such that the load is continuously incremented and decremented based on the results in step 806 . Hence, this leads to dynamic optimization of power harvesting.

As mentioned above, where the dc-dc converter 44 utilizes field effect transistors and accompanying transformers, the steps of changing the dc-dc converter settings in steps 805 and 807 may include changing the transformer used on the secondary tap to modify the load step appropriately. This is also the case where such a variable transformer is provided with an H-bridge as shown in Figure 2D. Alternatively, in such a case, the duty cycle of the transistors in the H-bridge can be adjusted to vary the load.

Figure 9 shows a flow chart illustrating the operation of a downhole unit 4a of the type described above.

In step 901 it is determined whether there is sufficient power to power the processors in the central unit 46 . If no, the process stays at this step until sufficient power exists.

When sufficient power exists, the process proceeds to step 902 where it is determined whether a command has been received or whether there is a requirement to send a predetermined set of data. If not, the process remains in this state of determining whether any action is required until action is required.

When action is required, the process proceeds to step 903 where data is retrieved from the sensor or from memory as required and the load presented by the energy harvester module between connections 41a is modulated to encode the data.

Separately at the wellhead, in step 904, the voltage potential of the wellhead is monitored and the data is decoded in the second microprocessor. The extracted data may then be exported or retransmitted to the client in step 905, eg via a seawater acoustic link or an umbilical link.

FIG. 10 shows a well facility including platform 1000 . The wellhead 1 is provided on the deck 1001 of the platform 1000 . In this case, the metal structure includes risers 1002 located between the mudline and deck 1001 . Production tubing 21 runs within riser 1002 and downhole. Casings 22, 23 are placed downhole. The innermost sleeve 22 is a continuation of the riser 1002 . The cathodic protection anode 3B is disposed on the platform structure 1000 . There will be electrical connections between the platform and the downhole structure 2 (casing and production tubing). This may be via the drilling template 1003 and/or via the wellhead, risers and other components such as riser guides. In such a case, it may be difficult to know where to form the upper connection of a collection arrangement of the type shown in Figures 1, 3, 4 or 6 for optimum performance. It will not always be known where the cathodic protection current will be injected into the conductive tube (segmented elongated member) extending down into the well. As mentioned above, it may be desirable to form an upper connection adjacent to where the CP current is injected. If one is looking for optimization, one option is to control this injection point, i.e. ensure the galvanic connection at a known point. Another option is to provide the system with multiple alternative upper connection points for the collection module and allow selection of the most efficient connection point after installation. Typically, in such a case, the power delivery system will be mounted with multiple upper cable connections to the metal structure, and the best performing one is selected by operating a switch, eg under the control of the central unit.

Signal, device and sensor options

A number of specific signaling techniques are described above. For the avoidance of doubt, it should be noted that in systems of the current type, many different signal transmission techniques may be used, alone or in combination, in portions of the signal channel. Accordingly, wireless signals may be transmitted in at least one of the following forms: electromagnetic, acoustic, inductively coupled tubing, and encoded pressure pulses, and references herein to "wireless" refer to such forms unless otherwise indicated.

Unless otherwise specified, signals may include control signals and data signals. The control signals can control downhole equipment, including sensors. Data from the sensor may be transmitted in response to the control signal. Furthermore, data acquisition and/or transmission parameters, such as acquisition and/or transmission rate or resolution, may be varied using suitable control signals.

Pressure pulsing includes the use of positive pressure changes and/or negative pressure changes and/or changes in the flow rate of fluids in the tubular space or annulus to go from/to another well/into the wellbore, from/to another well/into the wellbore A method of communicating a location and at least one of the surface of a well/bore.

Coded pressure pulses are pressure pulses in which a modulation scheme has been used to encode commands and/or data within pressure changes or flow rate changes, and transducers are used within the well/wellbore to detect and/or generate said change, and/or use electronic systems within the well/bore to encode and/or decode commands and/or data. Accordingly, pressure pulses used with the well/in-wellbore electronic interface are defined herein as encoded pressure pulses. An advantage of encoded pressure pulses as defined herein is that they can be sent to an electronic interface and can provide a greater transmission rate and/or bandwidth than pressure pulses sent to a mechanical interface.

Where encoded pressure pulses are used to transmit the control signal, a variety of modulation schemes can be used to encode the control signal, such as pressure change or rate of pressure change, on/off keying (OOK), pulse position modulation (PPM) , Pulse Width Modulation (PWM), Frequency Shift Keying (FSK), Pressure Shift Keying (PSK), Amplitude Shift Keying (ASK), a combination of modulation schemes such as OOK-PPM-PWM. Transmission rates for coding pressure modulation schemes are typically very low, typically less than 10 bps, and may be less than 0.1 bps. Encoded pressure pulses can be sensed in static or flowing fluids, and can be detected by directly or indirectly measuring changes in pressure and/or flow rate. Fluids include liquids, gases, and multiphase fluids, and can be static control fluids, and/or fluids produced from or injected into a well.

Wireless signals can enable them to pass through obstacles such as plugs or the annular sealing device when they are secured in place. Accordingly, wireless signals may be transmitted in at least one of the following forms: electromagnetic, acoustic, and inductively coupled tubing.

EM pulses/acoustic pulses and encoded pressure pulses use the well, borehole or formation as the transmission medium. The EM signal/acoustic signal or pressure signal can be sent from the well or from the surface. If provided in a well, the EM signal/acoustic signal would be able to travel through any annular sealing device, but for certain embodiments it may travel indirectly, eg around any annular sealing device.

Electromagnetic and acoustic signals are useful because of their ability to transmit through/through annular sealing equipment without special inductive coupling tubing infrastructure, and for data transmission, the amount of information that can be transmitted compared to encoded pressure pulses Normally higher, especially when receiving data from wells.

Where inductively coupled tubing is used, there are normally at least ten, and often more, individual lengths of inductively coupled tubing that are joined together in use to form a string of inductively coupled tubing. They have integral conductors and can be formed into tubulars such as oil tubing, drill pipe or casing. There is inductive coupling at each connection between adjacent lengths. Inductive coupling tubing that can be used is available from NOV under the trademark Intellipipe.

Therefore, EM signals/acoustic signals or pressure wireless signals can be transmitted as wireless signals over relatively long distances, up to at least 200m, optionally more than 400m or more, which is a clear benefit over other short-range signals. The inductive coupling tube provides this benefit/effect through the combination of an integral wire and inductive coupling. The distance traveled may be longer, depending on the length of the well.

Data and commands within the signal may be relayed or transmitted by other means. Accordingly, wireless signals may be converted to other types of wireless or wired signals, and optionally relayed in the same manner or by other means, such as hydraulic lines, electrical lines, and fiber optic lines. For example, the signal may be transmitted over a first distance, such as more than 400 meters, via a cable, and then a smaller distance, such as 200 meters, via acoustic communication or EM communication. In another embodiment, encoded pressure pulses can be used to transmit them for 500 meters and then hydraulic lines to transmit them for 1000 meters.

In addition to wireless methods, non-wireless methods can also be used to transmit signals. The distance the signal travels depends on the depth of the well, often wireless signals, including repeaters, but excluding any non-wireless transmissions, travel greater than 1000 meters or greater than 2000 meters.

Different wireless signals may be used in the same well for communications traveling from the well toward the surface, and communications traveling from the surface into the well.

The wireless signal may be sent directly or indirectly to the communication device, for example using in-well repeaters above and/or below any annular sealing device. Wireless signals can be transmitted from the surface or from a wireline/coiled tubing (tractor) section probe at any point in the well, optionally above any annular sealing device.

Acoustic signals and communications may include transmission of vibrations through the structure of the well, including tubulars, casing, liner, drill pipe, drill collars, tubing, coiled tubing, sucker rod, downhole tools; via fluids (including via gas) Transmission, including transmission through fluids in uncased sections of the well, in tubulars, and in annular spaces; transmission by static or flowing fluids; mechanical transmission by wireline, slide wire, or continuous rod; transmission by grounding; transmission by Wellhead equipment transmission. Communication by structure and/or by fluid is preferred.

Acoustic transmission can be at subsonic (<20Hz), sonic (20Hz-20kHz) and supersonic frequencies (20kHz-2MHz). Preferably, the acoustic transmissions are sound waves (20Hz-20khz).

Acoustic signals and communications may include frequency shift keying (FSK) and/or phase shift keying (PSK) modulation methods, and/or higher-level derivatives of these methods, such as quadrature phase shift keying (QPSK) or quadrature Amplitude Modulation (QAM) and preferably incorporates spread spectrum techniques. Typically, they are adapted to automatically tune the acoustic signal transmission frequency and method to suit well conditions.

Acoustic signals and communications can be unidirectional or bidirectional. Piezoelectric transducers, moving coil transducers or magnetostrictive transducers may be used to transmit and/or receive signals.

Electromagnetic (EM) (sometimes referred to as Quasi-Static (QS)) wireless communications are normally in the following frequency bands: (selected based on propagation characteristics)

sub-ELF (extremely low frequency) <3Hz (normally above 0.01Hz);

ELF 3Hz to 30Hz;

SLF (Super Low Frequency) 30Hz to 300Hz;

ULF (Ultra Low Frequency) 300Hz to 3k Hz; and,

VLF (Very Low Frequency) 3kHz to 30kHz.

An exception to the frequencies above is EM communications using tubes as waveguides, in particular, but not only when the tubes are filled with gas, in which case frequencies from 30kHz to 30GHz can typically be used, depending on the tube size , the fluid in the tube and the communication range. The fluid in the tube is preferably electrically non-conductive. US 5,831,549 describes a telemetry system involving gigahertz transmission in gas-filled tubular waveguides.

Sub-ELFs and/or ELFs are useful for well-to-surface communications (eg, over distances over 100 meters). For more local communications, eg less than 10 meters, VLF is useful. The nomenclature used for these ranges is defined by the International Telecommunication Union (ITU). EM communications may include sending communications by one or more of: imposing a modulated electrical current on one elongated member and using ground as a return; transmitting electrical current in one tube and providing a return path in a second tube; using Second well as part of current path; near-field transmission or far-field transmission; creates a current loop within part of well metalwork to create a potential difference between metalwork and ground; uses spaced contacts to create Electric dipole transmitters; use of toroidal transformers to impose current in well metalwork; use of insulating subs; coil antennas to create modulated time-varying magnetic fields for local transmission or transmission through formations; well casings Transmission inside the pipe; use of elongated members and grounds as coaxial transmission lines; use of pipe fittings as waveguides; transmission to the outside of the well casing.

It is especially useful to impose a modulated current on an elongated member and use ground as a return; create a current loop within a portion of the well metalwork to create a potential difference between the metalwork and ground; use a spacer contacts to create an electric dipole emitter; and, a toroidal transformer is used to force a current in the well metalwork.

A number of different techniques can be used in order to advantageously control and direct current. For example, one or more of the following: use insulating coatings or spacers on well tubulars; select well control fluids or cements inside or outside of well tubulars to conduct or electrically insulate from tubulars; use high permeability spirals Tubes to create inductance, and thus impedance; use insulated wire, cable, or insulated elongated conductor for a transmission path or part of an antenna; use tubes as circular waveguides, using SHF (3GHz to 30GHz) bands and UHF (300MHz to 3GHz) )frequency band.

A variety of means for receiving the transmitted signal may be used, which may include: detecting current flow; detecting potential differences; using dipole antennas; using coil antennas; using toroidal transformers; using Hall effect or similar magnetic fields Detector; uses a section of well metalwork as part of a dipole antenna.

Where the phrase "elongated member" is used, for the purposes of EM transmission, this can also mean any elongated electrical conductor, including: liner; casing; tubing or fittings; coiled tubing; sucker rods; steel cable; drilled pipe; slide wire or continuous rod.

The gauge may include one or more of a number of different types of sensors. The or each sensor may be coupled (physically or wirelessly) to a wireless transmitter, and data may be transmitted from the wireless transmitter above the annular sealing device or towards the ground. The data may be transmitted in at least one of the following forms: electromagnetic, acoustic and inductively coupled tubing, especially acoustic and/or electromagnetic as described herein above.

Such short-range wireless coupling can be facilitated by EM communication in the VLF range.

The sensors provided can sense any parameter and thus can be any type of sensor including, but not necessarily limited to, such as temperature, acceleration, vibration, torque, movement, motion, cement integrity, pressure, orientation and inclination, load, various Various types of fitting/casing angles, corrosion and erosion, radiation, noise, magnetic forces, seismic movement, stress and strain on the fitting/casing including twisting, shearing, compression, expansion, buckling and any form of deformation; chemical or radioactive tracer detection; fluid identification (such as gas detection); water detection, carbon dioxide detection, hydrate, wax, and sand production; and fluid properties such as (but not limited to) flow, density, water cutting, resistivity, pH, viscosity, bubble point, gas/oil ratio, hydrocarbon composition, fluid color or fluorescence. Sensors may be imaging devices, mapping devices, and/or scanning devices such as, but not limited to, cameras, video, infrared, magnetic resonance, acoustic, ultrasonic, electrical, optical, impedance, and capacitance. Sensors can also monitor equipment in the well, such as valve position or motor rotation. Furthermore, the sensors may be adapted to induce signals or parameters detected by incorporating suitable transmitters and mechanisms.

Instruments (especially sensors) may include storage devices that may store data for retrieval at a later time. In some cases, the memory device may also be retrieved and the data restored after retrieval. The memory device may be configured to store information for at least one minute, alternatively at least one hour, more alternatively at least one week, preferably at least one month, more preferably at least one year or more than five years.

Claims (23)

1. Downhole data communication apparatus for use in a well installation having a metal structure provided with a cathodic protection system such that there is an electrical circuit comprising the metal structure and a ground return due to the cathode To protect the system so that current flows around the ground return, the downhole data communication device includes: a first communication module positioned at a first location and comprising modulation means for modulating current at the first location to encode data; and A second communication module positioned at a second location spaced from the first location and comprising a detector for detecting the effect of modulating the current at the first location for extracting the data . 2. The downhole data communication tool of claim 1, wherein the modulation device is arranged to be at least one of: i) where the cathodic protection system is an external cathodic protection system, controlling the signal source of the external cathodic protection system to directly modulate the cathodic protection current applied to the metal structure; ii) modifying the connection between at least one anode of the cathodic protection system and the metal structure; and iii) Change the impedance of this circuit. 3. A downhole data communication apparatus according to claim 1 or 2, wherein the first communication module is arranged for positioning downhole. 4. A downhole data communication apparatus according to any preceding claim, wherein the second communication module is arranged for positioning downhole. 5. A downhole data communication apparatus according to any preceding claim, comprising a sensor module for sensing at least one parameter, wherein the first communication module is arranged to encode readings from the sensor module The data is sent towards the second communication module. 6. The downhole data communication tool of claim 5, wherein the sensor module includes a pressure sensor. 7. A downhole data communication apparatus according to any preceding claim, wherein the second communication module is arranged to provide data to the downhole apparatus based on data received from the first communication module via the second communication module . 8. The downhole data communication apparatus of claim 7, wherein the downhole equipment comprises at least one of: Downhole sensors; Downhole actuators; annular sealing equipment, such as packers or packer elements; valve; Downhole communication modules such as transceivers or repeaters. 9. The downhole data communication tool of claim 8, wherein the valve comprises at least one of: underground safety valve; Orifice flow control valve; orifice to annulus valve; annulus to annulus valve; orifice to pressure compensation chamber valve; Annulus to pressure compensation chamber valve; Through packer or packer bypass valve. 10. A downhole data communication apparatus according to any preceding claim, wherein at least one of the first communication module and the second communication module comprises a communication repeater for positioning in and downhole, and arranged for communicating with a first device beyond the wellhead using at least a wireless communication channel through the wellhead and arranged for communicating with a second device positioned in the well and thus positioned below the wellhead such that the communication repeater can Act as a repeater between the first device and the second device. 11. A downhole data communication apparatus according to any preceding claim, comprising a downhole electrical power harvesting module arranged for electrical connection between two spaced-apart locations in the well facility, and comprising a circuit arranged to, in use, collect electrical energy from a potential difference between spaced locations for collection, the potential difference serving as an input voltage, the collection module being arranged to supply power to at least one of the communication devices components are powered. 12. A downhole data communication apparatus as claimed in claim 11, wherein the first communication module is arranged to control a load generated by the collection module to generate all of the electrical current in the metal structure at the location of signal transmission described modulation. 13. The downhole data communication apparatus of claim 11 or 12, wherein the collection module is arranged to collect electrical energy from the dc current. 14. A downhole data communication system comprising a downhole data communication apparatus according to any preceding claim positioned in a well facility having a metal structure provided with cathodic protection . 15. A downhole data communication system for use in a well facility having a metal structure provided with a cathodic protection system such that there is an electrical circuit comprising the metal structure and a ground return due to The cathodic protection system, so that current flows back around the ground, the system includes a downhole data communication apparatus including: a first communication module positioned at a first location and including modulation means for modulating current at the first location to encode data; and A second communication module positioned at a second location spaced from the first location and including a detector for detecting the effect of modulating the current at the first location to Extract the data. 16. The downhole data communication system of claim 14 or 15, wherein the well is a subsea well. 17. The downhole data communication system of any one of claims 14 to 16, wherein the instrument comprises a downhole electrical power harvesting module electrically connected at two spaced-apart locations in the well facility and including a circuit arranged to collect electrical energy, in use, from a potential difference between the spaced locations for collection, the potential difference serving as an input voltage, the collection module being arranged to supply the communication device power to at least one component. 18. The downhole data communication system of claim 17, wherein the current flow within the portions of the metal structure in the region between the spaced locations for collection is in the same longitudinal direction. 19. A downhole data communication system according to claim 17 or 18, wherein there is an uninterrupted current flow path between the spaced apart locations for collecting, the uninterrupted current flow path at least partially through the metal structure . 20. The downhole data communication system of any one of claims 14 to 19, wherein at least one of the first communication module and the second communication module is positioned in a closed annulus of the well. 21. A downhole data communication system as claimed in any one of claims 14 to 20, comprising a pressure sensor arranged to monitor the reservoir pressure of the well. 22. A downhole data communication system as claimed in any one of claims 14 to 21, comprising a pressure sensor arranged to monitor the pressure in the annulus of the well. 23. A downhole data communication system as claimed in any one of claims 14 to 22, comprising a pressure sensor arranged to monitor the pressure in the closed annulus of the well.