GB2401617A - Communication using a control line - Google Patents

Abstract

A method of communication downhole involves the use of an insulated metallic, fluid carrying control line (5). The method involves applying signals to the control line (5) at one location and extracting signals at a second location. The signals are preferably electrical signals and the control line (5) passes through the well head (3) without electrical contact being made. The signals many be extracted from the control line (5) by inductive coupling.

Description

Downhole Communication This application relates to downhole communication,

particularly communication in a well having a metallic structure which includes an insulated meta]]ic fluid carrying control line.

There are currently quite a number of signal transmission techniques used in the downhole environment which make use of the meta]]ic structure of a well as the signa] channel. In genera] terms, these existing techniques make use of production tubing or casing as the signa] channel.

Two areas which give particular difficl]ties in operating such systems are, operating in cased sections of the we]] and extracting signals out from the top of the we]].

]5 In a large number of we]]s. a subsurface safety valve wi]] be provided, typica]]y a few hundreds of metres below the surface. lithe function of subsurface safety valves is we]] understood and in genera] terms they are provided to enable emergency shut off of the we]]. lypica]ly subsurface safety valves are hydrau]ica]]y operated and this means that there is typica]]y a fluid control dine or conduit provided from the surface down to the subsurface safety valve. This control dine is often insulated and typica]]y runs within the annulus defined between the production tubing and the well casing. In some instances the control circuit wi]] be gas operated rather than hydrau]ical]y operated. In such cases a fluid control line is still provided but clearly this then carries gas rather than liquid. s

It has been realised by the applicants that the existence of such a control line in the well can be of use in signal transmission within the well.

According to one aspect of the present invention there is provided a method of ]O downhole communication in a well having metallic structure which includes an insulated metallic, fluid carrying, control dine, the method comprising the steps of applying signals to the control dine at a first location and extracting the signals from the control line at a second location.

]5 According to another aspect of the present invention there is provided a downhole communication system for use in a well having metallic structure which includes an insulated metallic, fluid carrying, control line wherein the system comprises means for applying signals to the control line at a first location and means for extracting the signals from the control line at a second location and the control line acts as a signal channel.

Typically, a respective portion towards each end of the control line will be electrically and mechanically connected to other portions of metallic structure in the well so that a conducting loop exists of which the control line is a part.

In other cases however, one end of the control line may be electrically isolated from the surrounding structure, in particular isolation may be provided which allows the control line to pass through the well head without electrical contact being made to the well head.

Trying to extract (or apply) signals directly from (to) the control line after it has passed through the well head is attractive but poses significant difficulties.

It is difficult to successfully insulate the control line from the well head and provide the necessary pressure seal. It has been realised however, that it is not necessary to extract (or apply) signals from (to) the control line in such a way and this has allowed the development of more easily implemented techniques. ]5

The signals may be applied to and extracted from the control line either directly or indirectly. By this it is meant that in some cases there may be coupling means provided at the control line for applying and/or extracting signals but in other cases the signals may be conducted along the metallic structure and into the control line and/or conducted from the control line into other portions of metallic structure.

The signal may be extracted directly from the control dine via a respective inductive coupling. The signal may be extracted directly from the control line by detecting the signal across an isolation joint introduced into the control line.

Here an isolation joint serves to electrically isolate one portion of the control line from the portion on the other side of the joint whilst still enabling the control line to perform its primary function. lithe signal may be extracted from the control line using a voltage divider technique. In such a technique the potential difference across a conductor connected in series with a main part of the control line passing towards the transmitting location, is detected. The conductor connected in series may comprise a portion of the control line itself, an additional piece of control line provided in the well for this purpose or another component. In a preferred way of implementing this technique additional control line is wound around the production tubing within the casing with one end of this additional line connected to the well head in the usual way ]5 and the other end connected to the control line extending down into the well.

Electrical sensing connections can then be made to the additional portion of line towards each end.

lithe signal may be applied to the control line via a respective inductive coupling or one of the other configurations mentioned above, however, in currently preferred systems the signal is conducted into the control line from s other portions of magnetic structure.

The method may be a multidrop signalling method where signals may be applied to and/or extracted from the control line at a plurality of spaced locations. This is particularly appropriate where signals are applied to the control line and extracted from the control line via respective inductive couplings. It will be seen that duplex communication is possible.

The or each inductive coupling may comprise a generally toroidal magnetic material core carrying a winding and surrounding the control line so that in use the winding, core and control line together act as a transformer with the control line acting as a single turn winding.

In this application the expression generally toroidal is used to mean a generally ring-like structure which can be used to surround the control line, there is no suggestion that the ring itself need be of circular shape and nor is there any suggestion that the cross-section of the material making up the ring need be circular.

In a currently preferred set of embodiments the insulated control line is electrically connected, towards its lower end, to tubing in the well so that signals flowing in the tubing can flow into the control line. Further, in these embodiments, means for extracting signals from the control line are disposed towards an upper end of the control line. This arrangement of course also allows signals injected into the control line to flow out into the metallic structure downhole.

In a situation where there is a second well in the same region as the well in which signals are being transmitted, the method may comprise the step detecting signals due to noise seen in the second well and subtracting these from the signal extracted from the control line in the well in which signals are being transmitted.

In some embodiments, signals may be extracted from the control line by the steps of detecting the signals flowing in the control line at two spaced ]5 locations, subtracting the signals seen at a first of the locations from the signals seen at the other location and using the result of this subtraction as the output signal.

Typically the hydraulic control line will be provided in the well to supply hydraulic fluid to operate one or more subsurface safety valve. The purpose and function of subsurface safety valves is well understood and is not important to the working of the present invention. In the present system and method, use can be made of the fact that an insulated metallic hydraulic control line will often be found in the well between the wellhead and a subsurface safety valve.

The signals will typically be extracted from the control line at a region towards the location where the control line meets the wellhead. Conventional electrical cabling may be provided for carrying the extracted signals from the interior to the exterior of the well. The cabling may pass through the wel]head via a penetrator arranged to provide a pressure tight seal. It is significantly more straightforward to provide a pressure tight seal allowing cables to exit the well than it is to achieve the same in respect of a fluid carrying control line leaving the well.

An amplifier, for amplifying the extracted signals, may be provided locally at a point where the signals are extracted from the control line. This can allow the signals to be amplified in a relatively low noise environment before being fed to the exterior, for example, through the wellhead.

A coupling for extracting signals from the hose may comprise a current pick up coil which is arranged to be slipped over a free end of the control line. In installing such a pick up coi], the control dine may be disconnected from the wel]head to a]]ow the pick up cod] to be passed over the now free end of the control dine, after which the control line may be reconnected. A similar process may be used in inserting an isolation joint into the control dine or in introducing an additional length of control dine for use in a voltage divider.

Although not always specifica]]y mentioned above, it wi]] be appreciated that the communication system may comprise apparatus arranged for carrying out any one or any combination of the steps defined above. Sirni] ar]y, whilst the above is mainly written in terms of signals trave]]ing up the we]] and being extracted at the we]] head, the same or similar apparatus and the same or similar techniques may be used in transmission downwards, applying signals to the control dine at the we]] head. Thus, for example, additional lengths of dine, isolation joints and inductive coupling coils may be used to inject signals into the control dine at the we]] head.

Embodiments of the present invention wi]] now be described by way of example only with reference to the accompanying drawings in which: Figure 1 schematically shows a we]] including a downho]e communication system embodying the invention and which can be operated using a method which embodies the present invention; Figure 2 shows another well including a different downhole communication system which uses similar principles to that of the embodiment shown in S Figure 1; Figure 3 shows an alternative coupling means for extracting signals from and/or applying signals to a hydraulic control line in a system similar to that shown in Figure 1; and Figure 4 shows another alternative coupling means for extracting signals from and/or applying signals to a hydraulic control line in a system similar to that shown in Figure 1.

IS Figure 1 shows a well generally comprising production tubing 1 encased to a predetermined depth by casing 2. The production tubing I and casing are joined to a well head 3 at the surface or sea bed S. A subsurface safety valve 4 is provided within the production tubing 1 which can be used in a conventional manner to provide an emergency shut off of the production tubing if this is required. The subsurface safety valve 4 is hydraulically operated and a hydraulic control line 5 is provided for supplying hydraulic fluid from the surface S to the subsurface safety valve 4. The hydraulic control line 5 runs within the casing 2 and is also provided with its own electrically insulating sheathing. On the other hand however, the hydraulic control line 5 is mechanically and electrically connected to the production tubing 1 at one end and to the well head 3 at the other end.

In this embodiment, at a position remote from the hydraulic control line S. an isolation joint lJ is included in the production tubing 1. Transmitting means 6 is connected across the isolation joint lJ and arranged for applying signals to ]0 the production tubing 1. These signals can flow up the production tubing and any other metallic structure which is in electrical contact with the production tubing 1. As a consequence when a signal reaches the point in the production tubing 1 to which the hydraulic control line 5 is attached, part of the signal wild flow into and along the hydraulic control line S as indicated by the arrows.

A pickup module 7 is provided at a location towards the upper end of the hydraulic control line S. i.e. close to where the control line 5 meets the well head 3. The pickup module 7 primarily comprises a current pickup coil but in some instances may also comprise other electronic equipment such as an amplifier. Cabling 8 runs from an output of the pickup module 7 through a pressure tight penetrator 9 provided in the well head 3 and is connected to a detector 10.

In operation, as described above, signals from the transmitting means 6 travel up the production tubing 1 and hence along the hydraulic control line 5. When the signals pass through the control dine 5 in the region of the pickup module 7, corresponding signals are excited in the current pickup cod] which are then transmitted along the cabling 8 and can be detected by the detector 10. In this way it is possible to communicate between the transmission means 6 located downho]e and the detector 101ocated at the surface. Of course, there is little limit to the length of the cabling 8 as it leads away from the we]] head 3, so the detector JO can be positioned at any desirable location.

lithe pickup cod] of the pickup module 7 may comprise a generally toroidal magnetic material core which surrounds the hydraulic control line 5 and an appropriate winding which is wound around this core. lithe ends of the winding in such a case wi]] be connected to the cabling 8.

The pickup module 7 can be made within a relatively small size which is suitable for mounting on the hydraulic control line 5 in the space available within a we]]. lithe applicants have found that a pickup coil having a diameter of approximately 2.5 cm and an axia] length of 7.5 cm has proved satisfactory.

The module 7 can be simply mounted on the control dine 5 by the process of disconnecting the hydraulic control dine S from its connector at the we]] head 3, slipping the pickup cod] of the module 7 over the control dine 5 and then reconnecting the control dine 5 to the we]] head 3. s

As mentioned above, the hydraulic control dine is provided with its own electrically insulating sheathing which is typica]]y plastic. It is norma] ]y possible to place the pickup cod] directly over the hydraulic control dine S without any need to alter the sheathing at that point.

It has been determined that, in a typical we]], the impedance of the production tubing seen by signals as they reach the point where the hydraulic control dine branches off is of the order of 10 my, whereas the impedance seen in the control dine 5 is of the order of 50 Q. Therefore a re]ative]y sma]] proportion of the signa] flows up the control dine 5. On the other hand, however, once the signa] is in the insulated control dine 5 there is]itt]e further degradation of the signa] before it reaches the pickup coi]. Moreover, as the signa] is split at the point where the control dine 5 meets the production tubing 1, the noise in the signa] is also split by the same ratio. Therefore, since the signa] to noise ratio is the major factor in determining the ability to detect a signal, the sma]kr overa]] signal valve, is of little concern. Further, it wi]] be appreciated that, in the case of the signals flowing in the insulated hydraulic control dine S. the casing 2 provides a shielding against further noise being introduced.

Figure 2 shows another we]] including a downho]e communication system embodying the present invention. In this case the structure of the WE]] is substantia]]y the same as that described above and the same reference numerals have been used to indicate the corresponding features. Detailed description of the we]] structure is omitted for the sake of brevity.

In this case, again the insulated hydraulic control dine S is used for signa] transmission within the we]]. In this case, use is made of the fact that a current loop path is created by the meta]]ic structure of the tubing 1, the control dine S and the we]] head 3. The loop around which current may flow is indicated by the arrows in Figure 2. In this embodiment respective transceiver modules 101 ]5 are provided at opposite ends of the hydraulic control dine S. Each transceiver module 101 comprises an inductive coupling means 107 which surrounds the hydraulic control dine S at an appropriate location and which is connected to a respective transmitter receiver unit 106.

In this embodiment the transceiver modules 101 can communicate with one another along the hydraulic control dine S. That is to say signals can be transmitted from the lower end of the control line 5 towards the surface S and vice versa.

It will be realised that in practice more transceiver modules]01 could be provided at different locations along the hydraulic control dine if there were a need for this. Such transceiver modules 101 might for example, be used to measure pressure, temperature or another- parameter at different locations in the well under instructions received from the surface and transmit the resulting measurements back to the surface.

In alternatives two pickup modules may be located close to-one another at a location towards the top of the hydraulic control line, i.e. towards the point at which it meets the well head. The outputs from these two pickup modules can then be fed into a comparator which is arranged to detect the difference between the two signals and amplify this difference. The output of this comparator can then be fed to the exterior of the well via appropriate cabling.

This arrangement can have an advantage in that the amplification of the signal can be carried out within the shielded and relatively low noise environment which exists at the top of the well within the casing.

Figure 3 shows an alternative coupling for use in applying signals to and l5 extracting signals from the control line 5 in a system of the type shown in Figure 1. Here instead of the coupling module 7 including an inductive coupling, an isolation joint IJ is provided in the control line 5 at the region where it joins the well head 3. The isolation joint IJ is shown schematically and it will be understood that such a joint serves to electrically isolate the portions of control line 5 on either side of the joint whilst allowing the control line 5 to perform its normal fluid carrying function. In this case signals may be detected across/applied across the isolation joint IJ to allow the extraction of/application of signals to the control line 5. Simple electrical connections are made to the control line 5 either side of the joint IJ and cabling 8 leads away through a penetrator 9 in the well head 3.

In some implementations the isolation joint 1J may take the form of an insulating piece or length of hydraulic hosing - this might be a commercially available component, for example a piece of hydraulic system hose as would be used in a hydraulically driven arm or bucket on a construction vehicle. In another case the hose might be high resistance rather than isolating but could still be useful and might be used in a system that functions along the lines of the coupling described below with reference to Figure 4.

Figure 4 shows another alternative coupling. Here in place of an isolation joint, additional control line tubing 5a is provided at the top of the well and wrapped around the production tubing 1. In this way a significant length of control line Sa can be provided in a small space close to the well head 3. Simple electrical connections are made to the control line S at either end of the coiled additional S tubing Sa. Cabling 8 from these again leads away through a penetrator 9.

Signals may be detected across this coiled length of control line Sa and also applied to the line S across this coiled length Sa. It will be seen that the coiled length of control line 5a and control line proper (down to the subsurface safety valve) 5 act as a voltage divide. Therefore, the closer the match in length between the control line proper S and the additional line Sa, the better this technique will function.

A component other than standard control line can be used to give this voltage divider effect provided that the other component can withstand the conditions IS within the well casing. As an example, a shorter length of higher resistance special control line could be used so that a smaller additional length were required. It will be seen that in theory the additional control line Sa or other component are unnecessary as one electrical connection could be made near the well head 3 and the other at a significant distance downhole (say halfway along the control line S). In practice this is difficult, impossible or undesirable due to inaccessability and/or risk of damage. This makes the above ideas of particular utility.

In fitting an existing well with an isolation joint IJ or additional control line Sa to allow the above methods to be used, it should be possible to break the connection between the control line S and the well head 3, introduce the additional component and remake the connections.

In an alternative usable with each of the above techniques, the noise signal in a second well local to the well in which communication is taking place can be detected and this may be subtracted from the overall communication signal detected in the well of interest, to assist in extracting the signal of interest.

Claims (36)

1. A method of downhole communication in a well having metallic structure which includes an insulated metallic, fluid carrying, control line, the method comprising the steps of applying signals to the control line at a first location and extracting the signals from the control line at a second location.

2. A method according to claim 1 wherein a respective portion towards each end of the control line is electrically and mechanically connected to other portions of metallic structure in the well so that a conducting loop exists of which the control line is a part.

3. A method according to claim 1 wherein one end of the control line is electrically isolated from the surrounding structure.

4. A method according to claim 3 wherein isolation is provided which allows the control line to pass through the well head without electrical contact being made to the well head.

5. A method according to any preceding claim wherein the signal is extracted directly from the control line via a respective inductive coupling.

6. A method according to any one of claims 1 to 4 wherein the signal is extracted directly from the control line by detecting the signal across an isolation joint introduced into the control line.

S

7. A method according to any one of claims 1 to 4 wherein the signal is extracted from the control line using a voltage divider technique.

8. A method according to claim 7 wherein the potential difference across a conductor connected in series with a main part of the control line passing towards the transmitting location is detected,,

9. A method according to claim 8 wherein the conductor connected in series comprises a portion of the control line itself.

10. A method according to claim 8 wherein the conductor connected in series comprises an additional piece of control line provided in the well, which additional control line is wound around the production tubing within the casing with one end of this additional line connected to the well head and the other end connected to the control line extending down into the well.

11. A method according to any preceding claim wherein the method is a multidrop signalling method where signals may be applied to and/or extracted from the control line at a plurality of spaced locations.

12. A method according to claim 11 wherein signals are applied to the control line and extracted from the control line via respective inductive couplings.

13. A method according to claim 11 wherein each inductive coupling comprises a generally toroidal magnetic material core carrying a winding and surrounding the control line so that in use the winding, core and control line together act as a transformer with the control line acting as a single turn winding.

14. A method according to any preceding claim wherein there is a second well in the same region as the well in which signals are being transmitted, the method comprising the step of detecting signals due to noise seen in the second well and subtracting these from the signal extracted from the control line in the well in which signals are being transmitted.

1S. A method according to claim 14 wherein signals are extracted from the control line by the steps of detecting the signals flowing in the control line at two spaced locations, subtracting the signals seen at a first of the locations from the signals seen at the other location and using the result of this subtraction as the output signal.

16. A method according to any preceding claim wherein cabling is provided, which cabling passes through the wellhead via a penetrator arranged to provide a pressure tight seal.

17. A method according to claim 16 wherein an amplifier, for amplifying the extracted.signals, is provided locally at a point where the signals are extracted from the control line.

18. A method according to claim 12 wherein a coupling for extracting signals from the hose comprises a current pick up coil which is arranged to be slipped over a free end of the control line.

19. A downhole communication system for use in a well having metallic structure which includes an insulated metallic, fluid carrying, control line wherein the system comprises means for applying signals to the control line at a first location and means for extracting the signals from the control line at a second location and the control line acts as a signal channel.

20. A system according to claim 19 wherein a respective portion towards each end of the control line is electrically and mechanically connected to other portions of metallic structure in the well so that a conducting loop exists of which the control line is a part.

21. A system according to claim 19 wherein one end of the control line is electrically isolated from the surrounding structure.

22. A system according to claim 21 wherein isolation is provided which allows the control line to pass through the well head without electrical contact being made to the well head.

23. A system according to any one of claims 19 to 22 wherein the signal is extracted directly from the control line via a respective inductive coupling.

24. A system according to any one of claims 19 to 22 wherein the signal is extracted directly from the control line by detecting the signal across an isolation joint introduced into the control line.

25. A system according to any one of claims 19 to 22 wherein the signal is extracted from the control line using a voltage divider technique.

26. A system according to claim 25 wherein the potential difference across a conductor connected in series with a main part of the control line passing towards the transmitting location is detected.

27. A system according to claim 26 wherein the conductor connected in series comprises a portion of the control line itself.

28. A system according to claim 26 wherein the conductor connected in series comprises an additional piece of control line provided in the well which additional control line is wound around the production tubing within the casing with one end of this additional line connected to the well head and the other end connected to the control line extending down into the well.

29. A system according to any one of claims 19 to 28 wherein the system is a multidrop signalling system where signals may be applied to and/or extracted from the control line at a plurality of spaced locations.

30. A system according to claim 29 wherein signals are applied to the control line and extracted from the control line via respective inductive couplings.

31. A system according to claim 29 wherein each inductive coupling comprises a generally toroidal magnetic material core carrying a winding and surrounding the control line so that in use the winding, core and control line together act as a transformer with the control line acting as a single turn winding.

32. A system according to any one of claims 18 to 31 comprising cabling, which cabling passes through the wellhead via a penetrator arranged to provide a pressure tight seal.

33. A system according to claim 32 wherein an amplifier, for amplifying the extracted signals, is provided locally at a point where the signals are extracted from the control line.

34. A system according to claim 29 wherein a coupling for extracting signals from the hose comprises a current pick up coil which is arranged to be slipped over a free end of the control line.

35. A method of downhole communication in a well substantially as hereinbefore described with reference to the accompanying drawings.

36. A downhole communication system substantially as hereinbefore S described with reference to and/or as shown in any one of the accompanying drawings. l