GB2110270A - Drilling equipment and method - Google Patents

Abstract

In order to provide improved control of drilling, e.g. of oil and other wells, at great depths, devices for measuring operating parameters are located near the drill bit and the resulting electrical signals are transmitted up the drill stack by means of a cable 4 formed from a plurality of length of cable arranged in the drill tubes 1. Appropriate connectors are provided and the cable 4 is protected from drilling fluid by means of a sleeve 2. The use of electrical telemetry enables information to be transmitted virtually instantaneously the surface for corrective or control action to be taken as required, thus leading to considerable reduction in drilling times. The turbine driving the drill bit may be provided with a bypass or dump valve to unload the power to the turbine rapidly thus reducing the incidence of damage to the drill bit arising from its being driven unduly rapidly into hard material. in the case of rotary drilling, the torque applied to the bit would be cut. <IMAGE>

Description

SPECIFICATION Drilling equipment and method This invention relates to drilling equipment and methods. It is particularly applicable for drilling for oil or gas but may also be used for drilling geothermal wells or for mineral exploration.

When drilling for oil or gas, wells often have to be sunk for a depth of 1 5000 feet (say 4.5 km) or more. The nature and disposition of the various strata through which drilling takes place will be known from preliminary survey work.

Two basic systems are used in drilling today.

Rotary drilling employs a revolving "kelly" at the drill head, driving a number of drill tubes and terminating at the bottom of the hole with a drill bit. Drilling fluid is pumped through the drill tube bore and returns carrying chippings etc. with it through the annulus to the surface. The alternative, now finding increasing favour, is a drill pipe slowly rotated at the surface, to prevent striction, coupled with a main drive being supplied by a turbine activated by the drilling fluid. This turbine is situated above the drill bit.

To maintain a predetermined course, the direction (azimuth) and inclination (drift) must be accurately taken at regular short intervals. The method outlined requires the drill stack to be stationary for only a few seconds.

Should the drill stack have deviated, it will be necessary to correct its course.

Knowledge of the stratum through which the drill bit is passing is required and can be measured in the conventional way using resistivity and gamma count information.

It will be appreciated that the costs of drilling equipment and of maintaining personnel at drilling sites, which are increasingly frequently in inhospitable environments at locations remote from civilisation, run to many thousands of pounds sterling per diem. This is particularly true of many areas now being developed, where costs are significantly higher than in areas already developed. As a result of this, there is a strong economic incentive to proceed with drilling as rapidly as possible, while avoiding delays due to avoidable equipment damage.

In order to avoid this sort of damage, it is normal to drill slowly when approaching known hard strata, but since the positions of the strata and bit are not known to very great accuracy, wide tolerances have to be allowed and drilling may proceed slowly for considerable distances, leading to delays and consequent increased drilling costs.

Until comparatively recently drill bit technology has been such that a round trip has been necessary at intervals of a few days for replacement or maintenance of the drill bit, and during this work the opportunity has been taken for lowering instruments into the well to check the exact inclination and direction and to take conductivity or other similar readings on the surrounding strata at various depths. However, recent advances in drilling technology have made the drill bits more durable, so that routine inspection for maintenance or replacement is not necessary at such short intervals. However, regular monitoring of the parameters has made round trips necessary with the existing instrumentation, leading to a long delays in drilling.

Another high cost element in drilling is the drilling fluid. The drilling fluid forms a column of ever-increasing length as the drilling proceeds. In addition to driving the bit via a turbine, this column provides a hydrostatic pressure head which counteracts the subterranean pressures released when fluid layers are encountered during drilling. In order to provide an adequate resistance against blow out, the drilling fluid is made dense, for example by the use of some lead and/or mercury based materials. This makes the drilling fluid more expensive. It will be appreciated that the long delay in knowing of a pressure change at the bottom of the well means that a substantial margin of error has to be maintained, with a consequent increase in the cost of the drilling fluid, which has to be denser than might otherwise be the case.

In accordance with a first aspect of the invention, there is provided a drilling rig comprising a drill stack formed of a plurality of drill tubes, a drill bit located at the bottom end of the drill stack, a drive device for the drill bit, devices for measuring operating parameters at or adjacent the drill bit and for producing electrical signals representative of the instantaneous values of those parameters, and a cable attached to the drill stack for transmitting the said electrical signals along the drill stack.

By the use of cable telemetry, the signals can be received virtually instantaneously and appropriate action taken to cope with any changes detected. In particular, where a turbine is provided to drive the bit, the rig may include a bypass or unloading valve located near the drill bit to provide very rapid cut-off of power to the turbine or other drive means. The by-pass or unloading valve may be hydraulically operated under the control of an electrical signal transmitted along the said cable. The control signal may be generated automatically, but could be overridden by a human controller. In the case of rotary drive for the whole stack the drive motor output will be reduced. The signals passing from the lower end of the drill stack may be processed by a micro processor or computer and alarm and/or control signals may be generated automatically.Further, these signals may be recorded, transmitted on to another control center, or used for display/print out purposes.

In order to provide a readily extendable cable as the drilling progresses, the cable may be in the form of a length of cable permanently located in or on each drill tube and protected from drilling fluid passing up and down the drill stack. The lengths of cable are preferably joined end to end by connectors which make when the assembly of a drill tube to its neighbour is completed.

In accordance with a second aspect of the invention, there is provided a drill tube adapted to be fitted to axially adjacent similar drill tubes and having a length of electrical cable secured therein or thereon and provided with connectors to enable it to be connected to corresponding lengths of cable in the adjacent drill tubes as the tubes are mated together.

In order to enable correction to be made to the line of the drill stack, without the need for a round trip, one or more deviation elbows may be provided. Such an elbow will for instance allow deflection e.g. of 30 of the line of the drill stack to be achieved, by use of hydraulic rams. The elbow is guided and protected by guide sleeves outside the drill stack.

It is necessary to provide some electronic circuitry, preferably micro-electronic, at a zone adjacent the drill bit, to process the primary measured signals. In view of the adverse high temperature and pressure conditions prevailing at the depths envisaged, it is preferable, in order to enable normal circuitry to function, for a cooled zone, which is also pressure protected, to be provided. Cooling may be achieved by Peltier devices. Alternatively insulation and a heat sink may provide sufficient cooling.

In accordance with a third aspect of the invention, there is provided a method of drilling, by using a drilling rig comprising a drill stack formed of a plurality of drill tubes, a drill bit located at the bottom end of the drill stack, and a hydraulic drive device for the drill bit, including the steps of measuring operating parameters at or adjacent the drill bit and producing electrical signals representative of the instantaneous values of those parameters, and transmitting the said electrical signals along the drill stack by means of a cable attached to the drill stack.

The invention will be further described with respect to a preferred embodiment some details of which are shown in the accompanying diagrammatic drawings, in which: Figure 1 is a horizontal section through a drill tube showing the location of a cable length; Figure 2 is a partial vertical section showing the operation of an elbow.

Drilling is conventionally carried out using a drill stack comprising a number of drill tubes, e.g.

30 feet (9 metres) long and threaded to each other. It will be appreciated that drilling is often carried out at depths of up to several kilometres so that a large number of drilling tubes will be employed.

In the case of rotary drilling, the whole stack is rotated with a drill bit at the bottom. Alternatively, a turbine for driving the drill bit may be located at the bottom of the drill stack, and this turbine is driven by drilling fluid which is pumped down the drill stack, and returns back up the outside, under pressure supplied by a pump located adjacent the top of the drill stack. In accordance with the present invention a number of operating parameters are measured by measuring instruments located in the drill stack near the drill bit, and information from these measuring devices is transmitted up the stack in the form of electrical signals by means of a cable.

As can be seen from Figure 1, a drill tube 1 is shown as having an internal metal lining sleeve 2 provided with a groove 3 within which is located a cable 4. The cable has to be such as to withstand the temperatures and pressures likely to be encountered in operation and it is located in the groove 3 of the sleeve 2 to protect it from drilling fluids. It is located in this groove by means of adhesive and the drill tube is then shrink fitted onto the sleeve by heating the drill tube, introducing the sleeve, in a cold state, into it and allowing the drill tube to cool. Circumferential connectors and end sub-assemblies are then fitted to the end of the cable and the groove cavity is filled with oil and sealed. As each tube is added to the stack, the cable is connected to the cable already in the stack by means of the circumferential connector as the addition of the new tube is completed.The circuit is completed by connecting the top drill pipe to a take off slip ring mounted below the twist swivel.

As an alternative to shrink filling the drill tube onto a protective metal sleeve, the cable length may be introduced into a longitudinal groove formed in one surface of the drill tube and covered with a suitable resin which is heated to cover it and form a protective coating for the cable length.

It may be necessary for the cable to include boosters to maintain the signal to noise ratio at a sufficiently high level. Additional measurements may also be taken at intermediate points along the drill stack.

Should the turbine behaviour be such as to indicate that a hard stratum has been struck, so that turbine speed needs to be reduced immediately, an automatic operation may be provided of a turbine bypass or dumping valve so that a turbine torque is instantaneously reduced virtually to zero and the pump speed adjusted before the pump valve is closed to re-start the turbine at a reduced speed. In this way, damage to the drill bit is kept to a workable minimum. In the case of a rotary drilling, the torque applied to the drill bit would be cut.

In addition to these continuous measurements, instrumentation may be provided for making measurements of the angle of deviation from the vertical and the direction of the deviation from magnetic north. Such instruments may take any suitable form but preferred forms of such instrument are described in my co-pending applications numbered.. and .. ., and filed simultaneously herewith and entitled respectively "Device for measuring inclination", and "Remote Compass". In addition, an instrument may be provided to obtain the conductivity of the stratum in its immediate vicinity.

In order to enable corrections to be made to the line of the drill stack, one or more remotely operable deviation elbows may be provided as illustrated in Figure 2. The elbow shown in Figure 2 is provided in an otherwise normal drill tube which is divided into upper and lower portions 1 a and 1 b respectively by means of an overlap joint 1 2 allowing universal relative adjustment between the parts 1 la and 1 lobby means of a part spherical bearing 13. A number of hydraulic rams 14 are provided to adjust the relative positions of the upper and lower parts 1 a and 1 b to achieve the desired angle of correction.

The arrangement will have to be operated in ambient temperatures up to 2500C adjacent the drill bit, and measurement of temperature on a continuous basis will enable optimum drilling conditions to be maintained. The measurement of the ambient pressure adjacent the drill bit will enable less dense drilling fluids to be employed, thus resulting in a considerable cost saving. This arises from the fact that immediate recognition of a pressure change will enable rapid action to be taken at the surface to control the pressure balance, thereby reducing the required margin of error or safety factor.

By measuring the instantaneous torque or acceleration of the drill bit, any sudden change will give an indication of drill bit condition and/or of a new stratum being encountered. In order to acquire this information, the connector adjacent to the bit drive will need to have coupled to it strain gauges or a magnetic disc with a pick-up in the case of a turbine drive.

In order that the electronic circuitry should function reliably it is essential to protect it from the environmental conditions which will be encountered. Thus a protected environment of relatively low temperature, say below 700C, a pressure approximately 1 bar and limited vibration, say less than 1 g in any plane/frequency must be created. Temperatures likely to be encountered will be up to 2500C, with steady pressures up to 15,000 p.s.i., as well as considerable shock levels.

Temperature cooling can be obtained by use of single or multistage Peltier effect device, coupled with suitable thermal insulation. The use of micro circuitry where possible will be required as space and heat loss is a major consideration.

Small diameter holes in the main housing will be designed to provide adequate protection against the pressures to be encountered. It is essential that the minimum external junctions and seals are employed. A single cable will connect the circuitry to the surface. D.C. power will be supplied from the surface to the circuit adjacent to the drill bit via this cable as will various modulated control signals on suitable carrier frequencies. Information from the drill head will also be transmitted using the same principle. Thus it will be necessary to convert all information into a suitable modulated form for transmission.

The D.C. power supplied from the surface via the cable can be used in the electronics, and also to operate controls to tap the hydraulic power present in the drilling fluid being pumped down where greater power is required, e.g. for operating the rams on the adjustment elbow or for rapid operation of the pump valve and other moving parts.

Various modifications may be made within the scope of the invention. As an alternative to the tapping of the drilling fluid pressure, hydraulic operating pressure may be obtained from a hydraulic pump driven by a D.C. motor.

Claims (14)

Claims

1. A drilling rig comprising a drill stack formed of a plurality of drill tubes, a drill bit located at the bottom end of the drill stack, an hydraulic drive device for the drill bit, devices for measuring operating parameters at or adjacent the drill bit and for producing electrical signals representative of the instantaneous values of those parameters, and a cable attached to the drill stack for transmitting the said electrical signals along the drill stack.

2. A drilling rig as claimed in claim 1, in which the drill bit is driven by a turbine powered by the drilling fluid, comprising a bypass or unloading valve located near the drive for the drill bit to cut power to the drill bit.

3. A drilling rig as claimed in claim 1 or 2, in which the cable is formed from successive lengths of cable permanently located in or on the successive drill tubes and electrically connected together by appropriate connectors.

4. A drilling rid as claimed in claim 3, in which the connectors make in a circumferential manner when adjacent drill tubes as connected together.

5. A drilling rig as claimed in claim 3 or 4, in which the cable terminates in a slip ring at the top of the drill stack.

6. A drilling rig as claimed in any of claims 1 to 5, comprising at least one hydraulically operable deviation elbow between drill tube parts allowing limited adjustment of the line of the drill stack.

7. A drilling rig as claimed in any of the preceding claims, in which a cooled zone is provided in the region of the drill bit to mount circuitry associated with the measuring devices.

8. A drilling rig as claimed in claim 7, in which the cooled zone is cooled by one or more Peltier devices.

9. A drilling rig substantially as hereinbefore described.

10. A method of drilling by using a drilling rig comprising a drill stack formed of a plurality of drill tubes, a drill bit located at the bottom end of the drill stack, and a drive device for the drill bit including the steps of measuring operating parameters at or adjacent the drill bit and producing electrical signals representative of the instantaneous values of those parameters and transmitting the said electrical signals along the drill stack by means of a cable attached to the drill stack.

11. A drill tube adapted to be fitted to axially adjacent similar drill tubes and having a length of electrical cable secured therein or thereon and provided with connectors to enable it to be connected to corresponding lengths of cable in the adjacent drill tubes as the tubes are mated together.

12. A drill tube as claimed in claim 1 in which the cable is laid inside the tube and protected by a lining sleeve.

13. A drill tube as claimed in claim 12, in which the sleeve is fitted in the tube by shrink fitting the tube onto the sleeve.

14. A drill tube as claimed in claim 11, in which the cable is laid in a longitudinal recess in the tube and shielded by a cover formed in situ.

1 5. A drill tube substantially as hereinbefore described with reference to the accompanying drawings.