Title: Directional drilling apparatus

Field of the invention

This invention relates to drilling apparatus and in particular to the directional drilling of bore holes, for example in the fields of oil extraction, oil exploration, mineral exploration and geother al energy extraction. Th invention is applicable to apparatus which employs down hole turbines and motors for rotating a drill shaft, as well as apparatus for use in what is called rotary drilling, ie where a shaft in the form of a rotatable drill string extends from the ground surface to the drilling bit.

Summary of the invention

According to the invention drilling apparatus for drillin a bore hole comprises a drilling transmission shaft which is rotatably driven and which carries a drill bit, a component which is constrained against rotation with the shaft, a control stabiliser which engages the wall of the hole being drilled, the control stabiliser being either linked to said component so as to be constrained against rotation with the bit or being connected to the bit to rotate therewith, and actuating means which are operative to apply a radial force to the control stabiliser to generate a reactive force between the control stabiliser and the bore hole wall, which in turn generates a radial force on the drill bit for control of drilling course, the

actuating means not rotating with the shaft and bearing on a member which, is restrained against rotation by virtue of being connected to the component.

Where the invention is appled to apparatus which employs a down hole motor or turbine, the component is the housing of the down hole turbine or motor which is driven by a drilling fluid, the turbine or motor driving the transmission shaft. The control stabiliser is then linked to the housing of the turbine or motor, and the control stabiliser may include or be attached to a tubular member which is attached to the housing by means of a joint which prevents relative rotation between the housing and the tubular member in a direction parallel to the direction of rotation of the drilling transmission shaft but which allow lateral tilting movement or angulation between the housing and the tubular member. In this case, the actuator is preferably located in the annular space between the non-rotating control stabiliser (or tubular member) and a support tube which is cantilevered from the housing.

Where the control stabiliser is connected to the bit, the actuator is supported between two sleeves which are respectively mounted with respect to the shaft and the stabiliser by bearings.

The actuator may be in the form of a plurality of circumferentially spaced flexible tubes or bags which are supplied with hydraulic fluid in a controlled manner to generate a force at the bit of a required magnitude and radial direction, in order to control the drilling course. The actuator may be controlled by control means comprising sensing means for sensing the actual drilling course.

information storage means for storing a predetermined required drilling- course, and comparison means for comparing the sensed course with the required course and for delivering an error signal in dependence upon the comparison, the error signal being used to operate the actuator. The control means may be located, together with the actuator, in the radial space between the control stabiliser (or tubular member) and the support tube.

Two embodiments of drilling aparatus according to the invention, together with a modification, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows the first embodiment in diagrammatic section.

Figure 2 shows the second embodiment in diagrammatic half section.

Figure 3 is a sectional view on the line III-III of Figure 1, and

Figure 4 shows the modification.

Detailed description of the preferred embodiments

Referring to Figure 1, the apparatus comprises a down hole motor 10 driven by drilling fluid (water or mud) pumped from the surface. The motor 10 has a rotatable drive shaft 12 to which is attached one end of a hollow drilling transmission shaft 14 the other end of which carries a drill bit 16 which performs the cutting. After leaving the motor 10, the drilling fluid passes down the central

bore in the shaft 14, as shown by arrow 18, and is returned to the surface, together with chippings, by a flow path (shown by arrow 20) in the annular space between the apparatus and the bore hole wall 22.

A control stabiliser 24 is generally cylindrical but has three circumferentially spaced and radially projecting ribs 25 (Figure 3) which engage the bore hole wall 22. Gaps between the ribs 25 provide spaces for the flow indicated by the arrow 20. The control stabiliser 24 is rigidly attached to a tubular extension 26 connected, through a joint 28, to the housing of the motor 10. The joint 28 prevents relative rotation between the motor housing and the extension 26 in a direction generally parallel to the rotational axis of the drive shaft 12 but allows the extension 26 to tilt or articulate laterally with respect to the motor housing 10. The control stabiliser 24 is attached through a further articulating joint 30 to a short length of tube 31 attached through a third articulating joint 32, dynamic seal 34 and spaced bearings 31 to a flange 33 fixed to the shaft 14.

A support tube 36 is cantilevered from the motor housing 10 so as to be held against rotation. In the annular space between the tube 36 and the control stabiliser 24 is an actuator in the form of four circumferentially spaced bags 38 capable of being individually pressurised by hydraulic fluid. The annular space between the stabilisers (or the extension 26) and the tube 36 also accommodates an electronic control means 40 which monitors drilling and controls the individual pressurisation of the bags 38 in order to generate a radially outwardly directed force on the control stabiliser, this force having a desired radial direction and magnitude in dependence upon

the commanded correction to the drilling course. The radially outwardly directed force applied by the bags 38 to the control stabiliser 24 causes a reactive force to be applied to the control stabiliser by the bore hole wall. This in turn causes a lateral force to be exerted on the drill bit by the edge of the bore hole being drilled by the bit, and this force controls the drilling direction.

It will be appreciated that no attempt is made to bend the shaft 14 which is comparatively rigid. The bags 38 generate a lateral force which results in the drill bit being urged more forcibly in a lateral direction against the bore hole wall being drilled. Control ^' of the radial direction and magnitude of the force generated in the bags 38 enables the drill bit 16 to follow a desired predetermined course programmed into the electronic control means.

The bags 38 are similar to the flexible tubes or bags disclosed in the applicants' EP 0209318, and the control means 40 may be similar to the control means in this European Patent Specification.

The control means does not rotate with the -shaft 14 but is held against rotation in the same manner as the bags 38, ie being attached to a member or members linked to the motor housing 10.

In the second embodiment shown in Figure 2, the control stabiliser 24 rotates with the bit 16: this avoids the stabiliser 24 becoming jammed in the bore hole, which can happen in the arrangement of Figure 1. The stabiliser of Figure 2 has the same cross-sectional shape as that of Figure 1, ie as shown in Figure 3.

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Referring to Figure 2, the rotatable drive shaft 14 is connected by means of an adaptor 42 to the bit 16. In comparison with Figure 1, the stabiliser 24 and bearings 31 are interchanged. Hence, in Figure 2 the control stabiliser 24 is connected by a dynamic seal 34, spaced bearings 31 and angulation joint 32 to a sleeve 42 which surrounds the actuator bags 38. The sleeve 42 is connected by an angulation joint 28 to a further sleeve 44 which is rigidly attached to housing 10. The sleeve 44 is mounted on the shaft 14 by spaced bearings 46.

On its radially inner side, each bag 38 may be mounted on a cantilevered extension (like sleeve 36, Figure 1) projecting from the housing, or may (as indicated in Figure 2) be mounted on a cylindrical sleeve 48 by spaced bearings 50.

It will be appreciated that, instead of being mounted on sleeve 36, the bags 38 in Figure 1 may be supported on a sleeve and bearings like those shown at 48, 50 in Figure 2.

The electronic control means 40 in Figure 2 are located in the annular space between the non-rotating sleeve 44 and the shaft 14, and the electronic control means 40 are mounted on the non-rotating sleeve 44.

Towards the right hand side of Figure 2, a sleeve 52 is connected, through respective angulation joints 54, to the stabiliser 24 and the adaptor 42. The joints 54 allow tilting and also transmit drive, so that the stabiliser 24 is rotatably driven with the bit 16.

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In each of Figures 1 and 2 the actuator bag 38 and the electronics 40_are prevented from rotating with the bit because they are linked to the housing 10. An alternative is to employ a member which is prevented from rotating within the bore hole by an anti-rotation device. Figure 4 shows an example of this modifica ion.

Referring to Figure 4, a stabiliser 56 has a tubular extension 58. Respective ends of this component are threaded and may be incorporated in a drilling string driven from the surface. Alternatively, the left hand end may be connected to the shaft 12 of Figure 1 and be driven by a down hole motor.

A cylindrical sleeve 60 surrounds the extension 58 and is mounted thereon by spaced dynamic seals 62 and bearings 64. On its radially outer periphery, the sleeve 60 carries a plurality of circumferentially spaced springs 66 which engage the bore hole wall 22 and act to restrain the sleeve 60 against rotation while the stabiliser 56 and extension 58 rotate. The sleeve 60 is therefore held against rotation and to this sleeve may be attached the sleeve 26 as in Figure 1 or a sleeve 42 as in Figure 2.

Figure 4 shows the modification as a module which can be inserted in an existing drill string or may be attached to the lower end of a shaft 12 driven from a down hole motor or turbine 10. It will be appreciated that the construction of Figure 4 need not be in the form of a module. For example, the extension 58 may be constituted by the upper portion of the shaft 14 in Figure 1, in which case the sleeve 26 would be linked to the sleeve 60. Similarly, if the modification of Figure 4 were applied to the construction of Figure 2 the upper end of the shaft 14

would form the extension 58 and the sleeve 44 would then be restrained -against rotation by being connected to the sleeve 60.