GB2230288A

GB2230288A - Device for steering a drill bit

Info

Publication number: GB2230288A
Application number: GB9005509A
Authority: GB
Inventors: Trevelyn Moeller Coltman
Original assignee: TRANSBOR
Current assignee: TRANSBOR
Priority date: 1989-03-13
Filing date: 1990-03-12
Publication date: 1990-10-17
Also published as: GB9005509D0; CA2011972A1; DE4007907A1

Description

=1 z 1 - "DEVICE FOR STEERING A DRILL BIT" THIS invention relates to a

device for steering a drill bi t.

A common problem encountered in the art of deep drilling is the tendency of a drill bit to wander of f course. This is caused by factors such as the inherent flexibility of the extended drill string, and by the drill bit crossing transition zones between harder and softer rock layers, expecially at an acute angle.

The present invention seeks to provide a device for maintaining the drill bit on its predetermined course.

1 The invention provides a device for steering in a drill hole a drill bit carried at the leading end of a drill string element having an axially oriented passage for conveying flushing fluid to the drill bit during drilling, comprising a body located rotatably on the element, a series of pistons radially movable on the body and adapted to be actuated by' the flushing fluid, sensing means to sense when the drill bit wanders off a predetermined course, and control means responsive to the sensing means operable to control the flow of f luid to one or more of the pistons, thereby urging the piston or pistons towards the wall of drilled hole being drilled.

Preferably, the control means is further operable to allow one or more of the pistons which has been urged towards the wall of the drilled hole to retract after having redirected the drill bit.

The invention further provides an electric generator which is powered by the rotation of the element relative to the body, the generator in turn powering the control means.

In a preferred form of the invention, the control means comprises a motor which drives valve means.

Preferably, the pistons are urged against resilient shoes, which in turn bear against the wall of the drilled hole, preventing movement of the body relative to the element.

- 3 In the accompanying drawings:- Figure 1 shows a longitudinal section through the drill string device of the invention, Figure 2 shows a cross-section at the line A-A on Figure 1; and Figure 3 shows a cross-section at the line B-B on Figure 1.

The illustrated drill steering device 10 features a hollow drill string element 12 having a tube-shaped body 14 located rotatably on the element, and an end cap 16 fixed to the leading end of the element 12. An axially oriented passage 22 runs through both the element and the end cap 16 f or conveying flushing fluid in the direction of arrow 23 to the drill bit during drilling. The fluid returns back from the cutting face in the annulus 25 between the wall of the hole 27 and the steering device 10.

The drill string element 12 is provided with a female threaded socket 18 at its leading end which is coupled with the corresponding male threaded end 19 of a drill bit. The end cap 16 is equipped with a male threaded end 20 for coupling with a corresponding female threaded socket (not shown) of a further similar drill string element. In this manner, the drill steering device 10 is inserted between two rod pipes of a drilling string in which torque and flushing fluid are conveyed to a drill bit.

- 4 A series of pistons 24 a to f are arranged in cylinders 26 spaced equally in rows about the outer surface of the body 14. The pistons 24 a to f bear against resilient shoes in the form of leaf spring strips 28 mounted in grooves 30 located on the outer surf ace of the body 14. Each group of cylinders 26, which are disposed radially outwardly relative to the body 14, communicate with the passage 22 via first and second supply cavities 32 and 33. The second cavity entrance is located on a shoulder 34 where the passage 22 broadens into the socket 18. An annular plate valve 36 having an aperture 38 between the first and second supply cavities 32 and 33 is located rotatably on the element 12.

The plate valve 36 is sandwiched between an end face 40 of the body 14 and an opposing shoulder f ace on the drill string element 12. Face load on the valve plate 36 is maintained by a spring element 44 seated on a face 46 at the trailing end of the cap 16 which bears against a thrust plate 48, located at the opposite end of the body 14.

An electric generator 50 is mounted adjacent the thrust plate 48. The generator 50 has a rotor 52 mounted on the central shaft of the string element 12, and a stator 54 partly surrounding the rotor 52 and mounted on the body 14. Electrical power is generated by rotation of the drill string element 12 relative to the body 14. The body is prevented from rotation in the drill hole by the leaf springs 28, which bear against the walls 27 of the drill hole, and also serve to protect the pistons 24 by covering them, thereby preventing them from fouling against the walls of the hole.

The generator 50 -powers a servo-motor 58 housed in an oil-filled pressure compensated motor cavity 60. The motor drives a pinion 62 which turns the valve plate 36. Sensing means in the form of instrumentation 64 for the detection of deviation of the drill steering device from a predetermined path, is housed in a series of instrumentation cavities 66 located in the body 14. Each cavity has a plug 68 to protect the instrumentation against drilling fluid and high pressures.

In operation, the steering device works in the following manner. The instrumentation 64 detects when the drill steering device 10 wanders off a predetermined path, and sends a signal to the servo-motor 58 via a cable gland 70. The servo-motor 58 responds by turning the plate valve 36 an amount determined by the signal so that the aperture 38 in the valve registers with the first and second cavities 32 and 33. If the steering device is deviating in the direction indicated by the arrow 72 in Figure 3, the aperture 38 will register with the first and second cavities which communicate with the cylinders 26a.

Flushing fluid passing through the passage 22 in the direction of the arrow 23 will thereby be permitted to pass through the first and second cavities 32 and 33 and into the cylinders 26a. The pressure of the flushing fluid in the cylinders 26a urges the pistons 24a outwardly relative to the body 14 towards the walls of the hole, as can be seen in Figure 3, thereby forcing the leaf spring strip 28 against the hole walls, and moving the steering device 10 in the opposite direction to the direction of deviation 72. The instrumentation 64, on sensing that the steering device 10 is back on course, sends a signal to the servo motor 58, which in turn rotates the plate valve 36 so that the aperture 38 moves out of alignment with the supply cavities 32 and 33, thereby blocking off the flow of pressurized i flushing fluid to the cylinders 26a. Excess pressurised fluid in the first supply cavity 32 and in the cylinders 26a escapes through the vent hole 78, as the resilient action of the leaf spring 28 causes the pistons to return inwardly back to their normal position in the cylinders 26a, and pressure between the fluid in the supply cavity 32 and the annulus 25 is equalised.

Each of the cylinders 26 a to f have their own supply vents. Deviation of the steering device in another direction, such as that indicated by the arrow 76, will result in the aperture 38 in the plate valve 36 being brought into communication with the vent supplying the cylinder 26c, thereby causing the piston 24c to be urged outwards. The plate valve may have more than one aperture, allowing any two or more of the pistons to be operated-simultaneously.

The invention, in using equal area pistons, makes use of the phenomenon that there exists a difference in pressure between the flushing fluid flowing down through the passage 22 towards the bit, and the returning fluid in the annulus 25. The device is so designed that the force exerted by the flushing fluid in the cylinders on one side of' the pistons 24 exceeds the counter-force exerted by the leaf spring and the return fluid on the opposite side of the pistons 24.

The invention enjoys the advantage that it makes use of existing sufficiently powerful hydraulic forces which are readily available in situ to hold the steering device on course. Electro-mechanical means are only used to regulate the hydraulic forces.

1 - 7

Claims

A device, f or steering in a drill hole a drill bit carried at the leading end of a drill string element having an axially oriented passage for conveying flushing fluid to the drill bit during drilling, comprising a body located rotatably on the element, a series of pistons radially moveable on the body and adapted to be actuated by the flushing fluid, sensing means to sense when the drill bit wanders off a predetermined course, and control means responsive to the sensing means operable to control the flow of f luid to one or more of the pistons, thereby urging the piston or pistons towards the wall of the hole being drilled.
2.

The device claimed in claim 1 in which the control means is operable to allow one or more of the pistons which has been urged towards the wall of the hole to retract after having redirected the drill bit.
The device claimed in either one of the above claims including an electric generator which is powered by rotation of the element relative to the body, the generator in turn powering the control means.
4.

The device claimed in any one of the above claims in which the control means comprises a motor and valve means driven by the motor.
5. The device claimed in any one of the above claims in which the pistons are urged against resilient shoes which in turn bear against the wall of the hole, thus preventing movement of the body relative to the element.

6 A device for steering a drill bit substantially as herein described with reference to the accompanying drawings.

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