Drilling Devices

Abstract

Control means for fitting at the lower end of a drill pipe adjacent drilling means to control directional drilling comprise servo means for changing the drilling angle and further servo means for turning the control means with respect to the drill pipe axis in order to reorientate the device without changing the drilling angle. The control means also comprise means for programming and/or controlling both servo means by signals set in, or transmitted from, above ground.

Description

This invention relates to control means for drilling devices of the type used, for example, in the directional drilling of oil wells with a drill bit mounted at the lower end of a drill pipe or "string" and rotatable about an axis inclined to the longitudinal axis of the lower end of the pipe.

Such drilling devices at present in use have a fixed inclination (hereinafter referred to as the "drilling angle") with respect to the drill pipe axis and the complete device is in use rigidly fixed at the lower end of the pipe. Thus in order to drill in a different direction it is necessary either to reorientate the drill by turning the pipe or to withdraw the complete drill string and replace the device by one with a more appropriate drilling angle. It is difficult to estimate the angle through which the lower end of the drill string will turn as a result of turning the top end through a given angle, and having to withdraw the complete drill string to engage the device at frequent intervals wastes considerable time of a costly drilling rig. The object of the invention is to provide a device with which this difficulty and waste of time are materially overcome.

According to the invention control means for fitting at the lower end of a drill pipe adjacent drilling means to control directional drilling comprises servo means for changing the drilling angle (hereinafter referred to as "angle servo means"), further servo means for turning the control means or at least a portion thereof in use coupled to the drilling means with respect to the drill pipe axis in order to reorientate the device without changing the drilling angle (hereinafter referred to as "orientating servo means"), and means for programming and/or controlling the servo means by signals from above ground.

The control means may be directly attachable to driving means for the drill bit, which will normally comprise a so-called "mud" motor which obtains its power from the flow of drilling mud along the drill pipe. Alternatively the control means and drilling means may be manufactured as a unit, in which case the invention provides a drilling device including the driving means for the drill bit and the aforesaid control means.

The control means may include, or be adapted to attach to, a means of generating hydraulic power or electrical power, or both, to provide power for the servo means and associated circuitry. Preferably the electrical power generator or the hydraulic power generator or both are also driven by a separate mud motor. Alternatively, particularly when the control means are embodied in a drilling device unit including the drilling means, the generator may be coupled to the mud motor which drives the drill bit.

Preferably the control means incorporates electronic means for measuring the components of the earth's magnetic and/or gravitational fields, providing outputs which combine these measurements in a certain manner as defined by fixed signal processing within the control means or by remote drilling instructions, or by a combination of both. The mathematical basis of the determination of the inclinations and angular position of the sensing unit, from the sensor readings, is described later in this specification.

Drilling instructions may be given to the control means either by manual presetting of electrical controls before the control and drilling means are lowered into the well, or alternatively remotely by means which provide a communication link between the surface and the control means and which are dropped down the drill pipe. Such means are hereinafter referred to as "a programme carrier," and the carrier may be settable to command specific servo angles or to provide on/off instructions, for example when the drilling angle is movable by the angle servo from zero to a predetermined limit of say 3.degree. but is not adjustable to intermediate positions below that limit. Means may be provided to ensure that when it reaches the drilling device the programme carrier locates accurately in the angular sense with respect to a programme receiver embodied in the device at the trailing end thereof. The programme receiver identifies the specific command or commands set into the carrier, and these commands may be defined by the angular positions of bar magnets adjustably mounted at the leading end of the carrier and the adjusted positions of which are sensed by flux gates or Hall effect devices in the receiver.

A directional drilling device in accordance with the invention and mounted on the lower end of a drill string will now be described, by way of example, with reference to the accompanying drawings. In the drawings:

FIG. 1 is a diagram showing the device attached to a drill pipe and a drill bit,

FIG. 2 is a diagram showing the method of alignment of a programme carrier of the device with respect to the drill pipe, and

FIG. 3 is a block diagram of orientating servo means of the device.

The device 1 comprises six sections disposed in line axially of the device and through which the drill mud passes, the trailing end of the device being rigidly attached to the bottom pipe section of the drill string 2. The leading section in this embodiment comprises a mud motor 8 which drives the drill bit 7 and is disposed immediately adjacent angle servo means 3 operable to set the drilling angle to zero, or alternatively to a fixed value which is typically 2.degree.. As the drilling angle is not adjustable to any other value the servo is controlled in an on/off mode by programming means as will be described.

The angle servo means 3 are immediately followed by an electrical generator 4 driven by its own mud motor, and this is in turn followed by an electrical measuring device 5. This device measures the components of the earth's magnetic and gravitational fields and derives outputs to control a following orientating servo means 6, whereby the latter are maintained at the position commanded by programme inputs from the surface or by preset inputs. The orientating servo 6 controls orientation of the leading end of the device 1, and hence of the drill bit 7, with respect to the bottom end of the drill string 2.

The trailing end section of the device comprises a programme receiver 9. It receives programming commands from a programme carrier 11 which provides a communications link between the surface and the drill. Angle and on-off commands are set into the carrier 11 by the mechanical positioning of magnets such as 10 (FIG. 2) at the leading end of the carrier which is then dropped down the drill string 2 and falls freely under gravity until it reaches the drilling device 1. A mule-shoe 12 at the leading end of the carrier 11 engages and locates with an inwardly projecting pin 13 in the bottom pipe section, whereby to orientate the program carrier 11 accurately with respect to the receiver 9. The latter incorporates magnetic field sensing devices which identify angular components and on-off commands set into the programme carrier 11. The angular component commands are used to control the orientation servo 6, while on-off commands are used to control the angle servo 3 and also may be used to ensure that the programme carrier 11 has located in the carrier position within the drilling device 1. The device may incorporate a mud bypass valve which is operated in the event of non-location of the programme carrier and which acts to bypass the main mud motor.

In the described embodiment, the device 1 provides a unit including the drilling motor 8 and the control means 3,4,5,6 and 9. However, it will be appreciated that the control means may be manufactured and supplied as a separate unit adapted for attachment to the drilling means.

It will also be appreciated that the described device enables accurate directional control to be accomplished without the need for continual reorientation, the electronic measuring device ensuring that the drill follows the command direction irrespective of torque wind-up in the drill string or any tendency of the drill bit to wander. The fact that it is unnecessary to estimate the pipe wind-up angle is a very great advantage, as is the facility to adjust the drilling angle to zero without coming out of the hole. Previously when changing from directional to straight drilling it has been necessary to withdraw the complete drill string and fit a new drilling device. In fact, with the present device it is only necessary to come out of the hole when it is necessary to change the drill bit.

The trailing end of the programme carrier 11 has a projection 14 which can be engaged by a grab shoe on a line dropped down the drill string, thus enabling the programme carrier to be withdrawn for command resetting. While it is withdrawn a measuring instrument can be dropped down which provides information as to the inclination and direction of drilling.

Present methods of orientating drills rely on some sensing means (usually photographed pendulous floating magnet assemblies), transmission of results to the surface (usually by physically transporting the film to the surface and then processing it) and then repositioning the drill by turning the upper end of the drill pipe. Developments of sensing means to enable electrical transmission of orientation data have enabled drills to be continuously orientated while drilling but these developments require the use of a transmission system (usually a conducting cable) and control is still carried out by turning the upper end of the drill pipe.

The orientating servo 6 of the present device uses the outputs from the sensing elements to rotate the drill with respect to the lower end of the drill pipe 2. Continuous orientation while drilling is achieved without the need for any type of transmission link to the surface. A block diagram of the orientation servo 6 is shown in FIG. 3, to which reference will now be made.

Outputs or combinations of outputs are taken from the sensing elements and become inputs to a resolver R. This resolver may be either electro mechanical or electronic in its operation, but in either case it combines the input signals as follows:

If one input is e1 and a second input is e2, then the output is a function of e1, e2 and an angular input such that

Output = e1 sin.alpha. + e2 cos.alpha.

The resolver output is fed to a servo amplifier the output of which drives the orientating servo motor. This motor drives through a reduction gearbox to orientate the drill. As the drill motor turns the sensing elements also turn and the sensing element outputs change. The drill motor continues to turn until the resolver output is zero.

If the resolver inputs are .DELTA.1 and .DELTA.2, as defined by equations (11) and (12) of the mathematical analysis set out at the end of this description, and the resolver input angle is .phi..sub.i, then the servo will orientate the drill such that

.DELTA.1 sin .phi..sub.i + .DELTA.2 cos .phi..sub.i = 0

substituting from said equations (11) and (12) gives

sin .theta. cos .phi. sin.phi..sub.i - sin .theta. sin .phi. cos .phi..sub.i = 0 which has a solution

.phi. = .phi..sub.i

Thus the orientation servo positions the drill to the input angle .phi..sub.1.

In like manner if the resolver inputs are .psi..sub.1 + .beta..DELTA..sub.1 and .psi..sub.2 + .beta..DELTA..sub.2 then, using equations (15) and (16) of said mathematical analysis the orientation servo will position the drill to an input angle .psi..sub.B .

The resolver input angle .phi..sub.i or .psi..sub.B may be either preset before the drill is lowered into the well or may be set into the servo by means of the programme carrier.

The mathematical basis of the control equations used in the programmable directional drilling device is set out below.

1. Definition of Axes

System of axes defined by suffix "O" is earth fixed with OX.sub.o horizontal and directed towards magnetic north, OY.sub.o horizontal and directed towards magnetic east, OZ.sub.o vertical and directed upwards.

Axes OXYZ, with no suffix, are fixed in the body of the survey instrument.

2. Definition of Rotations

Starting with OXYZ and OX.sub.o Y.sub.o Z.sub.o coincident, OXYZ is rotated about axis OZ by an angle ".psi. , " which will be defined as the AZIMUTH ANGLE.

From its new position, OXYZ is further rotated by a PITCH ANGLE ".theta." about the axis OY.

The final rotation is again about the axis OZ by an angle ".phi., " which will be defined as the ROLL ANGLE.

3. co-ordinate Transformation Matrices

From standard classical mathematics of co-ordinate transformation, the relationship between any vector .fwdarw.A.sub.x in the earth-fixed frame and the same vector .fwdarw.A.sub.x in the instrument frame is

.fwdarw.A.sub.x = [B].sup.. .fwdarw.A.sub.X

where [B] is a three by three matrix defined by the three rotations as follows: ##SPC1##

Note: for conformal transformations [B ].sup.-.sup.1 = [B]* where [B].sup.-.sup.1 is the inverse of [B]and [B]* is the transpose of [B] .

Thus: ##SPC2##

4. The Gravity Vector in Instrument Axes

Let the gravity vector referred to the earth-fixed axes be ##SPC3##

and the gravity vector referred to the instrument axes be ##SPC4##

which when multiplied out gives:

g.sub.x = g sin .theta. cos .phi. (1) g.sub.y = -g sin .theta. sin (2) i.

g.sub.z = -g cos .theta. (3)

Measurements of the components of gravitational force on a mass in the instrument can yield quantities .DELTA..sub.1, .DELTA..sub.2 and .DELTA..sub.3 where

.DELTA..sub.1 .alpha. g.sub.x (4) .DELTA..sub.2 .alpha. (5) ub.y

and .DELTA..sub.3 .alpha. g.sub.z (6)

5. The Earth's Field Vector in Instrument Axes

If the horizontal and vertical components of the earth's field are H.sub.h and H.sub.v respectively, then the field vector referred to the earth-fixed axes is ##SPC5##

Let the field vector referred to the instrument axes be ##SPC6##

which when multiplied out gives:

H.sub.x = H.sub.h cos .psi.cos .theta.cos .phi.-H.sub.h sin .psi.sin.phi.+H.sub.v sin .theta.cos.phi. (7) H.sub.y = -H.sub.h cos.psi.cos.th eta.sin.phi.-H .sub.h sin.psi.cos.ph i.-H.sub.v sin.theta.sin. phi. (8)

H.sub.z = H.sub.h cos .psi.sin.theta. - H.sub.v cos.theta.

Equations (7) and (8) are rearranged as follows

H.sub.x -H.sub.v sin.theta.cos.phi.= H.sub.h cos.psi.cos.theta.cos.phi.-H.sub.h sin.psi.sin.phi. (9) H.sub.y +H.sub.v sin.theta.sin. phi.=-H.sub.h cos.psi.cos.th eta.sin.phi.-H .sub.h sin.psi.cos.ph i. (10)

Measurements taken in the instrument yield three quantities .psi..sub.1, .psi..sub.2 and .psi..sub.3 where

.psi..sub.1 .alpha. H.sub.x

.psi..sub.2 .alpha. H.sub.y

and .psi..sub.3 .alpha. H.sub.z

From equations (1) to (6), we derive

.DELTA..sub.1 .alpha. sin .theta. cos .phi. (11) .DELTA..sub.2 .alpha. - sin .theta. sin .phi. (12)

Substituting equations (9) and (10) yields

.psi..sub.1 + .beta..DELTA..sub.1 .alpha. cos .psi.cos .theta. cos .phi. - sin .psi. sin .phi. (13)

.psi..sub.2 + .beta..DELTA..sub.2 .alpha. - cos .psi. cos .theta. sin .phi. - sin .psi. cos .phi. (14)

where .beta. is a constant.

For comparatively small values of .theta. (20.degree. > .theta. > 0) the rotations .psi. and .phi. may be considered to be in the same plane and the angle .psi. + .phi. is a good approximation to the angle between axes OX.sub.o and OX. This angle is defined as the BODY AXIS AZIMUTH ANGLE .psi..sub.B.

Then for .theta. < 20.degree.

.psi..sub.B .congruent. .psi. + .phi.

Equations (13) and (14) may then be rewritten. (cos .theta. taken to be 1)

.psi..sub.1 + .beta..DELTA..sub.1 .alpha. cos .psi..sub.B (15) .psi..sub.2 + .beta..DELTA. .sub.2 .alpha. -sin (16)...sub.B

Claims

I claim:

1. Control means for fitting at the lower end of a drill pipe adjacent drilling means to control the drilling angle and orientation of the drilling means for directional drilling, comprising first servo means for changing the drilling angle, further servo means for orientating the first servo means with respect to the drill pipe axis without changing the drilling angle, and means for programming and/or controlling both servo means by signals set in, or transmitted from, above ground, said control means including means for generating power to provide power for the servo means.

2. Control means for fitting at the lower end of a drill pipe adjacent drilling means to control the drilling angle and orientation of the drilling means for directional drilling, comprising first servo means for changing the drilling angle, further servo means for orientating the first servo means with respect to the drill pipe axis without changing the drilling angle, means for programming and/or controlling both servo means by signals set in, or transmitted from, above ground, a communication link between the surface and said control means, said link comprising a programme carrier whereby signals constituting drilling instructions may be conveyed to the control means, a programme receiver in the control means, attachment means on the programme carrier for lowering said carrier down the drill pipe, at least one magnet mounted on the lower end face of said carrier to approach the receiver, means for adjusting the angular position of the magnet on said lower end face to represent a specific drilling instruction, and means in the receiver sensitive to the positional adjustment of the magnet.

3. Control means according to claim 2, wherein means are provided to ensure that when the programme carrier reaches the control means it locates accurately in the angular sense with respect to the programme receiver in the control means.

4. Control means according to claim 2, wherein the programme receiver embodies at least one flux gate operative to sense the positional adjustment of the magnet.

5. A borehole drilling device comprising a substantially rigid drill pipe extending underground from adjacent the surface of the ground, drilling means at the lower end of the drill pipe, and control means at the lower end of the drill pipe adjacent said drilling means to control the drilling angle and orientation of the drilling means for directional drilling, said control means comprising first servo means for changing the drilling angle, further servo means for orienting the first servo means with respect to the drill pipe axis without changing the drilling angle, and means for controlling both servo means.

6. A borehole drilling device as claimed in claim 5, said control means including means responsive to the earth's magnetic and/or gravitational fields to control the drilling angle and orientation of the drilling means.