GB2282165A

GB2282165A - Directional drilling apparatus and method

Info

Publication number: GB2282165A
Application number: GB9318311A
Authority: GB
Inventors: Peter Allen
Original assignee: CAMBRIDGE DRILLING AUTOMATION; Cambridge Radiation Tech
Current assignee: CAMBRIDGE DRILLING AUTOMATION; Cambridge Radiation Tech
Priority date: 1993-09-03
Filing date: 1993-09-03
Publication date: 1995-03-29
Also published as: NO943218L; CA2130736A1; NO943218D0; GB9318311D0; DE4432408A1

Description

2282165 1 Title: Drilling apparatus and method

Field of the invention

This invention relates to apparatus for and a method of drilling using a drill string comprising coiled tubing.

Background to the invention

With regard to borehole course control, drilling using coiled tubing differs from normal drilling practice using a rotating drill string because, since the continuous drill string is beinq fed from a reel on the surface, it cannot be rotated.

Whilst drilling with a conventional rotating drill string and a down hole motor it is normal to have, integral with the motor, a fixed bend. This is shown in Figure 1 of the accompanying drawings. When a change of course is required the plane of the bend is adjusted from the surface by simply rotating the complete drill string until the new plane is achieved. When drilling then recommences with the drill string fixed, the course of the bore hole changes in the plane of the bend. The angular orientation of the plane of the bend is referred to as "toolface".

When the desired course has been achieved and drilling straight ahead is required, the drill string is continuously rotated, slowly, from the surface. The bend thus rotates and this results in a slightly oversize, but generally straight, bore hole.

The present invention is concerned with course control where the drill string incorporates coiled tubing and therefore cannot be rotated.

Summary of the invention

According to one aspect of the invention drilling apparatus comprises a drill string having coiled tubing which extends down a bore being drilled and which is uncoiled as drilling progresses, a leading end of the drill string carrying a drilling motor having a body and a bit rotatably driven with respect to the body, the bit and the body being out of alignment by a bend angle and adjustment means for effecting controlled rotation of the motor body with respect to the coiled tubing for control of drilling course.

The invention thus uses the torque reaction from the motor to achieve the required toolface for orientation and for providing a slow rotation for drilling straight ahead.

The adjustment means preferably comprise a brake for controlling relative rotation between the motor body and the coiled tubing. The brake is conveniently activated by pressure fluid, such as hydraulic fluid. In a preferred embodiment, the brake is a multi-plate brake actuated by a piston and cylinder driven by the hydraulic fluid from a hydraulic pump.

Preferably, the brake operates between the motor bodyr or an extension thereof, and a body of a control section which is attached, conveniently through the intermediary 1 of an adaptor, to the downstream end of the coiled tubing. The control section convenirntly accommodates control electronics, including a transducer for measuring the relative angular position of the motor body with respect to a body of the control section. The motor is preferably driven by pressurised mud conveyed through a central bore in the drill string.

In order to increase the torque available to rotate the motor body for course control, the motor drive shaft may be extended into the control section, where contollable retaining means are provided to lock rotationally the motor drive shaft with respect to the control section. The controllable retaining means may be a clutch or multiplate brake which may be controlled hydraulically or electrically.

According to another aspect of the invention there is provided a method of drilling using a drill string including coiled tubing and a drilling motor, comprising using the reaction torque of the motor to effect controlled adjusting rotation of the motor body with respect to the coiled tubing to effect control of drilling direction.

Two embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:Figure 2 is a diagrammatic view, partially in longitudinal section, of the first embodiment, Figure 3 is a diagrammatic view, partially in longitudinal section of the second embodiment, and Figure 4 shows, to an enlarged scale, part of the structure of Figure 3.

The drilling apparatus of the first embodiment has a drill string using coiled tubing the downhole end of which is shown at 10 in Figure 2. The coiled tubing is about 50 millimetres in diameter and, as drilling progresses, the coiled tubing is unwound from a reel at the ground surface. Because the coiled tubing is unwound from a reel, it cannot be rotated in the manner of a conventional drill string.

Figure 2 shows the structure connected to the downhole end of the coiled tubing. An adaptor 12 connects the coiled tubing to the body 14 of control electronics, this body being rotationally fixed to a sleeve 16 which is in turn fixed to a ring 18 incorporating bearings 20. The body 14 incorporates a further set of bearings 22, and the bearings 20 and 22 are positioned to support, for controlled rotation, a hollow shaft 24 which is an extension of a housing 26 of a downhole motor 28 shown in the lower part of Figure 2. The structure to the left of the arrow 30 in Figure 2 rotates with respect to the motor body 26. The extremity of this rotating structure is constituted by a bit 32 which provides the cutting action. Spaced seals 34, 36 seal the shaft 24 with respect to the ring 18 and body 14, respectively.

The body 26 of the motor incorporates a bend, i.e. a change of direction which is illustrated at 38 in Figure 2 and which typically is an angular misalignment of 1 or 2 degrees between the rotational axis of the bit 32 and the - 5 longitudinal axis of the major part of the body 26. It will be appreciated that controlled rotation of the tubular extension constituting the shaft 24, and therefore the motor body 26, with respect to the body 14 of the control electronics, adjusts the toolface for control of drilling direction. The motor 28 is driven by a flow of pressurised mud which is delivered to the motor through a central bore in the drill string, the mud flow being indicated by the line 40 in Figure 2.

Relative rotation between the shaft 24 and the body 14 of the control electronics is governed by means of a multiplate brake 42 which is accommodated in the annular space between the sleeve 16 and the shaft 24 and which has alternating plates projecting from these respective components. The braking effect is altered by means of an annular piston 44 movable in an annular cylinder 46 pressurised by hydraulic fluid derived from a hydraulic pump 48, either driven electrically or mechanically from the motor body extension. A change in hydraulic pressure causes a change in the thrust applied to the plates of the brake 42 and hence a change in the level of braking torque.

A transducer accommodated in the control electronics measures the relative angular position of the shaft 24 and the body 14. Information from this transducer also allows the relative rotational speed of the shaft 24 and body 14 to be calculated. Reference number 48 shows an electrical wireline communicating with the control electronics.

When course changing is required, the toolface necessary to change drilling direction onto the new course is computed. To set this toolface the body 26 of the motor is allowed to rotate slowly with respect to the body 14 of the control electronics, the torque being derived from the reaction of the motor, until the required toolface is achieved, when the brake 42 is applied so as effectively to lock the shaft 24 with respect to the body 14 of the control electronics. Control of this process is through valves which supply oil to the piston and cylinder arrangement. The speed of rotation of the body 26 whilst setting the toolface is controlled by a closed loop control system, the actual speed being derived from the angular position transducer.

When the desired drilling course has been achieved and drilling straight ahead is required, the motor body 26 is allowed to rotate continuously, resulting in a slightly oversize borehole being drilled in a straight ahead direction.

One possible deficiency with the embodiment of Figure 2 is that the torque available for rotating the motor body 26 may be insufficient to effect the required rotation of the motor body. For example, this can happen if the drill string becomes "keyseated" and insufficient weight on the bit can be applied in order to generate bit torque. The modification of Figures 3 and 4 is intended to overcome this possible deficiency.

In Figures 3 and 4 parts corresponding to those of Figure 2 have been given the same reference numerals. The embodiment of Figures3 and 4 differs from that of Figure 2 in that in Figures3 and 4 the rotatable shaft 50 of the mud motor 28 is extended through the hollow shaft 24 forming an extension of the motor body and into the control section. Restraining means 52 are then provided, y either by a clutch or multi-plate brake, to lock the motor shaft 50 to the body 14 of the control section. Under these circumstances the maximum mud motor torque is available to rotate the body 26 of the motor, and hence maximum use is made of the reaction torque in this embodiment.

Claims

1. Drilling apparatus comprising a drill string having coiled tubing which extends down a :n 0 bore being drilled and which is uncoiled as drilling progresses, a leading end of the drill string carryinc, a drilling motor having; a body and a bit rotatably driven with respect to the I IM body, the bit and the body being out of alignment by a bend angle and adjustment means for effecting controlled rotation of the motor body with respect to the coiled tubing for control of drilling course.

2. Drilling apparatus according to claim 1, wherein the adjustment means comprise a brake & CI for controlling relative rotation between the motor body and the coiled tubing.

Drilling apparatus according to claim 2, wherein the brake is activated by pressure fluid, such as hydraulic fluid.

4. Drilling apparatus according to claim 3), wherein the brake is a multiplate brake actuated =5 -- by a piston and cylinder driven by hgdraulic fluid from a hydraulic pump.

5. Drilling apparatus according to any of the preceding claims, wherein the brake operates between the motor body, or an extension thereof. and a body of a control section which is attached to the downstream end of the coiled tubine,

6. Drilling apparatus according to claim 5, wherein the control section accommodates & I" control electronics, including a transducer for measurin. the relative angular position of the In It, motor body with respect to a body of the control section.

7. Drilling apparatus according to claim 5 or 6, wherein in order to increase the torque Z=.

available to rotate the motor body for course control, the motor drive shaft is extended into the control section, where controllable restraining means are provided to lock rotationally the 9 motor drive shaft with respect to the control section.

8. Drilling apparatus according to claim 7, wherein the controllable restraining means are a clutch or multi-plate brake.

9. Drilling appartus according to any of the preceding claims, wherein the motor is driven t> t> by pressurised mud conveyed through a central bore in the drill string.

10. A method of drilling using a drill string including coiled tubing and a drilling motor, comprising using the reaction torque of the motor to effect controlled adjusting rotation of Z:> the motor body with respect to the coiled tubing to effect control of drilling direction.

11. Drilling apparatus or a method of drilling substantially as herein particularly described C> with reference to Figure 2 or Figures 3 and 4 of the accompanying drawings.