Directional Drilling Means

Abstract

A drilling head attachable to a drill pipe for directional drilling in a borehole is arranged to be rotatable with respect to the drill pipe and to be held in required orientation against the drill reaction torque, by clutch means or by a torque balancing force. A counter torque may be set up by rotation of the drill pipe and applied as the torque balancing force. A loaded pump driven by the drill pipe is suitable for producing the counter torque, the loading being adjustable by restricting shunt flow or by varying the loading of an electricla generator driven by a hydraulic motor supplied by the pump. The orientation is measured as an angle in a gravitational and/or geomagnetic frame of reference in a control circuit including a sensor unit located in the drilling head, the control circuit being preset or programmed or subject to command from the surface to hold the head at the required orientation.

Description

FIELD OF THE INVENTION

This invention relates to directional drilling and to methods of and means for drilling and for directional control of drilling with a drilling head mounted at the lower end of a drill pipe or "string."

STATEMENT OF PRIOR ART

In one existing method of drilling bore holes, particularly for oil, a drilling head comprising a hydraulic motor or "mud motor" driving a drill bit is rigidly fixed at the lower end of the drill pipe, either aligned with or slightly inclined to the axis of the drill pipe at that end. Change of direction can be effected with an inclined head suitably orientated by rotating the drill pipe from the surface, although difficulty arises in setting the orientation due to "wind-up" in the drill pipe. For steering purposes it has been necessary to withdraw the drill pipe and to change the head.

Disadvantages of such a method can be avoided by providing for the changing of the inclination and/or the orientation of the drilling head in situ in the bore hole and by local servo means, the drilling head then for orientation being rotatable with respect to the end of the drill tube as described in the specification of my U.S. Pat. No. 3,713,500.

SUMMARY OF THE INVENTION

The present invention is concerned particularly with the orientation and control of orientation of a drilling head. According to the invention, a drilling head attachable to a drill pipe for directional drilling in a bore hole is arranged to be rotatable with respect to the drill pipe and to be held in required orientation against the drill reaction torque. In use, the drilling head, particularly a mud motor in a housing, tends to rotate bodily with respect to the working drill bit on the head and so to be power driven progressively to change its orientation. The head can be held in a required orientation and against further rotation, for example by clutching or by a torque balancing force.

The orientation may be measured as an angle in a gravitational and/or geomagnetic frame of reference in a control circuit including a unit located in the head containing sensors of earth field objects and the control circuit may be preset or programmed or subject to command from the surface to hold the head at a required orientation or sequence of orientations.

As a further feature of the invention a counter torque may be set up by rotation of the drill pipe and applied as the torque balancing force for holding the head in a required orientation. The counter torque may be the reaction torque in a loaded pump adapted to be driven by rotation of the drill pipe. The counter torque is then adjustable by varying the loading to reach a balanced torque condition at a desired orientation.

The load for the pump may be provided by a hydraulic motor in a closed fluid circuit with the pump and coupled to drive an electrical generator. The electrical load on the generator can then be varied electronically under the control of the control circuit. At the same time the generator may be arranged to supply the instrument power necessary for the control circuit.

Thus the invention also provides a method of or means for adjustably controlling the orientation of a drill motor at the lower end of a drill pipe in a bore hole, wherein the drill reaction torque upon the drill motor is opposed by a controlled torque derived from rotation of the drill pipe.

The controlled torque may be provided by an adjustable hydraulic torque-changing device interposed between the drill pipe and the drill motor. Rotation of the drill pipe relative to the drill-motor housing may be applied to pump hydraulic fluid in a circuit in which the resistance to fluid flow can be varied. The resistance to fluid flow may be provided by controlled pressure-reducing orifices or flow paths shunting the pump or by said hydraulic motor.

The invention further provides means for controlling the orientation of a drill motor carried at the drilling end of a drill pipe in a bore hole, wherein the drill reaction torque on the drill motor is conteracted by a torque-changing or torque-adjusting means adapted to be driven by rotation of the drill pipe and controlled by orientation measuring means associated with the drill motor. The torque-changing or adjusting means preferably includes a variably loaded electrical generator which generator supplies instrumentation power for the orientation measuring means controlling the loading of the generator.

The control means required for installation at the lower end of a drill pipe carrying a drill motor may comprise an orientation measuring unit including sensors of components of the earth magnetic and/or gravitational fields and a variable electrical or hydraulic resistive load controlled by said measuring unit whereby in use the load may be automatically adjusted for the purpose of providing a torque to balance the drill reaction torque at a required orientation of the mid-plane motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of the relevant parts of a drilling installation providing for the control of the orientation of a mud-motor at the lower end of a drill pipe in a bore hole,

FIG. 2 is a block diagram of one arrangement for controlling the orientation of a drilling head in the installation of FIG. 1,

FIG. 3 is a block diagram of an alternative arrangement for controlling the orientation, and

FIG. 4 is a cross-sectional view of a particular form of hydraulic pump which may be used in the installation of FIG. 1 with orientation control as in FIG. 2 or 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drilling arrangement as a whole is generally similar to that described in the specification of my aforesaid previous application in that it comprises, as shown in FIG. 1, a drill pipe string with a mud-motor 2 and drill bit 3 at the lower end. The mud-motor 2 in a housing 4 is adjustable in inclination by angle servo means 5 the mud-motor 2 and angle servo means 5 together with an electronic measuring device 6 including gravitational and/or magnetic sensors being axially rotatable as a structure at the end of the lowermost pipe section 7 of the string 1 and constituting the drilling head 8 to be controlled in orientation. The structure constituting the drilling head 8 includes a pipe section 9 axially rotatable within the pipe section 7 and having a suitable form of thrust bearing therein, diagrammatically represented as a bearing 10. Preferably a pair of sealed tapered-roller-bearings are provided at or near the respective ends of the pipe-section 9 for rotation of that pipe section and to take the thrust and lateral loads. An orientating servo system is provided in a form to be described hereinafter and a programme receiver (not shown) may be included to receive drilling commands from a programme carrier lowered down the drill string 1 and arranged to come into predetermined alignment with the receiver.

During drilling, there is a reaction torque tending to rotate the rotatably mounted drilling head 8 and so to give rise to progressive orientation. The orientating servo system is arranged to hold the drilling head against the reaction torque and in required orientation determined by the measuring device 6 which establishes a frame of reference, and by commands injected into the measuring device. The latter controls the angle servo means 5 as in the aforesaid prior specification and it also controls the orientating servo system.

Thus the orientating servo system in its simplest form may consist of a power-operated clutch effective when the actual orientation reaches the demanded orientation, and such an arrangement will be further described hereinafter.

In the preferred embodiments, however, a counter torque is set up and the orientating servo system functions to balance the reaction torque and the counter torque at the demanded orientation. In order to provide the necessary input power for this purpose, provision is made at the surface for continuously rotating the drill pipe, the speed of rotation being preferably in the range of 25 to 50 r.p.m. The means for continuously rotating the drill pipe may be as already in use for rotating a drill string to reach a desired orientation of a conventional mud-motor-drilling head, namely a kelly comprising squared section of pipe 11 disposed above-surface and longitudinally movable, with the drill string, in a power-driven rotatable table 12 with a central square aperture. It will be noted that rotation of the drill pipe makes it possible to change the orientation of the drilling head in the reverse sense to change due to the drill reaction torque.

There are incidental advantages in providing for continuous rotation of the drill pipe. In conventional drilling with down-hole mud motors, the drill pipe requires to be restrained at the surface against rotation and the static state of the pipe increases the possibility of the pipe sticking in the bore hole. As well as minimising sticking of the pipe, rotation greatly reduces pipe friction along the hole axis and makes it much easier to apply pressure to the drilling bit in a smooth manner.

The counter torque is applied by interposing between the drill pipe 7 and the drilling head 8 a hydraulic controlled torque device. The latter is in the form of a hydraulic pump 13, body-mounted in the pipe section 9 with a clearance provided by ribs 14, and having an input shaft 15 coupled by means of an apertured transverse plate 16 to the drill pipe 7 to be driven thereby. The pump 13 is adjustably loaded to produce a controllable torque between the input shaft 15 and the pump body, that is, between the driving and reacting parts of the pump. Thus the body or reacting part of the pump 13 is rotatable and coupled to the drilling head 8 to apply the controllable torque in opposition to the drill reaction torque.

The working fluid for the pump 13 is contained in a closed circuit and an appropriate hydraulic fluid is chosen and conserved free from contamination.

The hydraulic pump 13 is of a kind suitable for use as a rotary torque-adjusting device. A constant-displacement pump, in which the fluid output is proportional to the rate of movement, is normally chosen. Preferably a peristaltic pump is used to ease sealing problems and may take the form shown in FIG. 4. Referring to FIG. 4, three or four rollers 20 are attached to an input carriage 21 and arranged to squeeze a spiral tube 22 of rubber, one end of the tube 22 being the hydraulic fluid input and the other the output. The rollers 20 are mounted on the carriage 21 to extend axially around the input or drive shaft 15 and within a cylindrical rotatable pump body part 24.

For varying the loading on the pump 13, the rate of fluid flow through the pump is subject to control by means of units such as units 25, 26, 27 (FIG. 1), coupled to measuring device 6. Thus the differential pressure across the pump is controlled and hence also the torque transmitted.

In one arrangement, illustrated by the block diagram of FIG. 2, the flow rate is controlled by a pressure-dropping valve system 30 through which the pump 13 discharges back to the input. The pump input shaft 15 rotates with the drill pipe 7 and the pump body is subject to the drill reaction torque, as will be clear from FIG. 1, the reaction torque being shown in FIG. 2 as applied to a shaft 31 representing the body fo the pump 13. For convenience in electrical control, the pressure drop in the load circuit of the pump 13 is produced in a series of constricted paths 32 in parallel and controlled by electrically operated stop valves 33. The path constrictions are conveniently provided by orifices in the stop valves. Four such valves 33 arranged to control binary weighted orifices can give a torque variation of 16 to 1 which is fully adequate for smooth control. A small electrical generator 34, for example, of the kind having a permanent-magnet rotor, is coupled between shafts 15 and 31 by gearing 35 to provide an instrumentation power supply. This supply is applied over a line 36 to measuring device 6 which rotates as part of the drilling head and controls the valves 33 according to the orientation of the drilling head.

In another and preferred arrangement, diagrammatically represented in FIG. 3, the pump 13 is shunted for fluid flow by a hydraulic motor 25 directly coupled to an electrical generator 26. By varying the value of a resistive load 27 connected across the generator output the generator loading is controlled and hence also the generator input torque, the loading of the hydraulic motor 25 and the flow rate through the pump 13. The use of a generator and electrical loading has the additional advantage of directly providing instrumentation power for the measuring unit 6 via a line 36a.

In the more simple arrangement above referred to, wherein the drilling head is clutched, under control of the measuring device 6, to a drill tube not subject to continuous rotation, the pump 13 of FIG. 1 is replaced by a hydraulic clutch, mud-pressure operated. Instrumention power is provided by a small generator driven by the drill motor or an auxiliary motor, and an electrically-operated relay controlled by the measuring unit 6 is provided for clutch operation.

Claims

I claim:

1. Drilling means for directional drilling in a borehole, comprising a drill pipe and a drilling head the orientation of which determines the direction of deviation of the borehole, a bearing by means of which said head is rotatably carried by the drill pipe for orientation, a tool-driving motor mounted in said head and a drilling tool coupled to the motor to be driven thereby so that, when the drilling tool is loaded in use, said head is subject to a tool reaction torque tending to rotate the head to change the orientation thereof, means for controllably counteracting the tool reaction torque and control means operative upon the counteracting means whereby the orientation of the head may be held at an adjusted setting.

2. Drilling means according to claim 1, wherein the control means comprises a measuring device within said head providing an output dependent upon the orientation of the head.

3. Drilling means according to claim 1, including means for continuously rotating the drill pipe during drilling, and wherein the counteracting means comprises a torque converter coupling the drill pipe to said head to provide a torque balancing force.

4. Drilling means according to claim 3, wherein the torque converter is a loaded pump.

5. Drilling means according to claim 4, including means for varying the pump loading to permit of balancing the drill reaction torque to hold the head at a set orientation.

6. Drilling means according to claim 5, wherein the means for varying the pump loading comprise a plurality of restricted paths in shunt to the pump and means for selectively opening and closing said paths.

7. Drilling means according to claim 5, wherein the means for varying the pump loading comprise a closed fluid circuit for the pump, a hydraulic motor in said circuit, an electrical generator coupled to be driven by said motor and a variable resistive loading for said generator.

8. A method for adjustably controlling the orientation of a drilling motor driving a drilling tool at the lower end of a drill pipe, including the steps of continuously rotating the drill pipe during drilling, deriving a variable torque from the rotating drill pipe, applying the derived variable torque to oppose the drill reaction torque to which the drilling motor is subject when the drilling tool is loaded in use, said drill reaction torque tending to change the orientation of said motor, and adjusting the derived variable torque to balance the drill reaction torque when the orientation has a set value and so to hold the drilling motor at that set value of orientation.