GB2408757A - Actuator Valve and Bias Unit - Google Patents

Abstract

The invention relates to an electrically controllable bi-stable actuator valve 20 for use in a bias unit of a steerable downhole drilling system. Actuators 20 are used to drive the pads 12, of the bias unit, between a retracted and an extended position so as to apply a side load to the unit and form a curve or dog leg. The bias unit comprises a plurality of actuators 20, operable under the application of fluid pressure 22, and a plurality of actuator valves arranged to control the supply of fluid pressure to the actuators 20, at least one of the actuator valves 20 is an electrically controllable bi-stable valve. The arrangement allows the timing, duration and order of the pads 12 being held in their extended positions to be controlled and where bi-stable valves are used the bias unit only consumes electrical power when the actuator valves 20 are being switched between their stable conditions.

Description

ACTUATOR VALVE AND BIAS UNIT

This invention relates to an actuator valve, and in particular to a bistable actuator valve suitable for use in a steerable downhole drilling system. The invention also relates to a bias unit for a steerable downhole drilling system incorporating such an actuator.

One well known steerable drilling system for use in the formation of wellbores comprises a bias unit haying a plurality of bias pads which are individually moveable between retracted and extended positions. Actuators are associated with the pads to drive the pads between the retracted and extended positions. The actuators typically take the form of drilling fluid or mud powered pistons to which drilling fluid or mud is supplied, under pressure, through a rotary valve the position of which is controlled by, for example, a roll stabilised control unit.

In use, when a curve or dog leg is to be formed, the valve is controlled so that the pads are moved between their retracted and extended positions, in turn, as the bias unit rotates so that the pad in its extended position is always located on the same side of the bias unit, in space, thereby applying a side load to the bias unit and any component secured thereto.

Bias units of this type have several disadvantages. For example, the system used to control the bias unit makes it very difficult to accurately vary the timing, duration or order in which the pads ofthe bias unit are moved. Further as the rotary valve must be physically connected to the associated control unit, the overall system is of relatively great length which is undesirable.

According to the present invention there is provided a bias unit comprising a plurality of actuators, each being operable under the application of fluid under pressure thereto to move an associated bias pad from a retracted position to an extended position, and a plurality of actuator valves arranged to control the supply of fluid under pressure to the actuators, wherein at least one ofthe actuator valves is an electrically controllable bi-stable valve.

Such an arrangement is advantageous in that the timing, duration and order in which the actuators are driven to hold the bias pads in their extended conditions can be controlled. Further, as each actuator valve is electrically controlled, only electrical connections are required between the actuator valves and a control unit associated therewith. Additionally, by using bi-stable valves, the bias unit need only consume electrical power when the actuator valves are being switched between their stable conditions, no power being consumed in holding the actuator valves in either of their stable conditions, and so is relatively efficient to use.

The actuator valve or each bi-stable valve is conveniently solenoid actuated.

In such an arrangement, an excitation coil is used to operate the bistable valve, to cause the valve member thereofto move between its stable conditions, and there is a risk of the fluid impinging upon and causing damage to the excitation coil.

Preferably, therefore, the excitation coil is provided within a protective housing to isolate the excitation coil from the fluid. Any wires and/or connectors connected to the excitation coil are conveniently also located within the protective housing. In order to minimise magnetic losses occurring as a result of the provision of the housing, the housing is conveniently of thin walled construction. One suitable material for the housing is stainless steel.

One potential disadvantage with bi-stable valves is that the control system associated therewith may lose track of the position occupied by the valve member thereof, for example if the valve fails to properly switch. In order to provide feedback to the control system, a position sensor may be provided to monitor the position occupied by the valve member. The position sensor could be a contact sensor, for example a micro switch, or a non-contact sensor, for example a Hall effect sensor. Another possibility is to monitor the operation ofthe excitation coil to ascertain whether or not an actuation or excitation ofthe coil has taken place, and to monitor changes in the load presented by the coil. If valve movement occurs, the load will change. No change in load signifies that, for some reason, the valve has failed to switch between its stable conditions.

According to another aspect of the invention there is provided an electrically controllable bi-stable valve suitable for use in the bias unit defined hereinbefore to control the supply of fluid under pressure to at least one of the actuators thereof.

Preferably, the bi-stable valve comprises a face valve member rotatable about an axis between a first position in which communication is permitted between an inlet and a first outlet, a second outlet being closed, and a second position in which the first outlet is closed and communication is permitted between the inlet and the second outlet.

The valve preferably includes an excitation coil, a housing being provided to protect the coil from damage due to the environment in which it is intended to operate. The housing is conveniently thin-walled and is preferably of stainless steel construction.

A sensor may be provided to allow the state of the valve to be sensed. The sensor could comprise a contact sensor, for example in the form of a micro-switch, or alternatively could comprise a non-contact sensor, for example in the form of a Hall effect sensor. A further alternative sensor may be arranged to monitor the operation of the excitation coil to provide an indication of the position occupied by the valve or switching thereof.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a bias unit; Figure 2 is a diagrammatic view of an actuator valve; Figure 3 is another diagrammatic view illustrating part of the actuator valve of Figure 2; and Figure 4 is a diagrammatic view of part of an alternative actuator valve.

The bias unit illustrated, diagrammatically, in Figure 1 comprises a housing upon which a number of bias pads 12 are pivotally mounted. Two bias pads 12 are visible in Figure 1, but it will be appreciated that the bias unit will typically include more bias pads than this, the bias unit typically including three or four bias pads 12. Each bias pad 12 is moveable between a radially retracted position (see the lower half of Figure 1) and a radially extended position (see the upper half of Figure 1). Actuators in the form of pistons 14 are provided to move the bias pads 12 between their retracted and extended positions. Each piston 14 is moveable within a corresponding bore 16 provided in the housing 20, the piston 14 and associated bore 16 together defining a chamber 18. Respective actuator valves 20 are provided to control the pressure of fluid located within the associated chamber 18. Each actuator valve 20 is a bistable valve arranged to allow the associated chamber 18 to communicate either with a fluid supply line 22 to allow fluid under relatively high pressure to be supplied to the chamber 18, or alternatively for the chamber 18 to communicate through a drain line 24 with the exterior ofthe bias unit to allow fluid to flow from the chamber 18. It will be appreciated that when fluid under relatively high pressure is supplied from the supply line 22 to the chamber 18, the associated bias pad 12 is urged towards its radially extended position, switching ofthe valve 20 to allow communication between the chamber 18 and the drain line 24 allowing the bias pad 12 to return to its retracted position.

The use of bistable actuator valves in the control of the operation or movement of the pistons 14 and bias pads 12 is advantageous in that it allows the manner in which the bias unit is operated to be accurately controlled. By way of example, the timing at which each bias pad 12 is moved from its refracted position to its extended position can be chosen by the operator at will. Further, the duration over which the bias pad 12 occupies its extended position can be chosen by the operator. Additionally, the order in which he bias pads 12 are moved between their retracted and extended positions may be altered if desired.

Another possibility, by rapid switching of the control valve 20, is that the magnitude of the biassing load applied to the bias unit 10 by the engagement of one or more of the bias pads 12 with the surrounding formation may be controlled independently of the pressure at which fluid is supplied through the supply line 22.

In a typical bias unit, each bias pad is usually held in its extended position for a relatively long duration whilst the bias unit rotates through a relatively large angle.

As a result, the biassing load achieved by the extension of the bias pad does not occur in a single direction, the direction of the biassing load varying as the bias unit rotates. In the present invention, each bias pad may be moved to its extended position for only a very brief duration. Such momentary actuation of each bias pad 12 results in the application of a momentary actuation force which, by appropriate control, acts in the desired, single direction rather than over a range of directions.

As a result improved directional control over drilling may be achieved.

By using bistable actuators in the bias unit, the operating efficiency of the actuator valves can be relatively high. Each of the actuator valves only expends energy when switching between its stable states, no energy being used in holding each actuator valve in one or other of its stable conditions. Each actuator valve is conveniently electrically operated, and it will be appreciated that the improved operating efficiency achieved by the use of bistable valves results in a significant reduction in the electrical power required to drive the system.

The bistable actuator valves 20 used in the arrangement of Figure l may take a range of forms. By way of example only, the valves could be of the type described and illustrated in US 2003/0168112. However, the use of valves of this type is thought to be disadvantageous in that wear and erosion may severely restrict the operating life of the valve. Further, in view of the high operating pressures used in downhole drilling applications, a large actuator force would be required in order to move the valve member from one state to another, and the size of the components necessary to achieve such large actuator forces would place severe design constraints upon the operating system. There is further the risk that the rocker valve member of the US 2003/0168112 arrangement may, in use, move away from the valve seat under high shock loadings which could cause erroneous movement of the bias pads from their retracted to their extended positions at inappropriate times, and could permanently damage the valve.

Referring next to Figure 2 there is shown, diagrammatically, a bistable actuator valve 20 suitable for use in the bias unit of Figure 1. The bistable actuator valve of Figure 2 comprises a rotatable face sealing valve member 26 which is in sealing engagement with a seating surface of a valve seating member 28. The valve seating member 28 is provided with first and second openings or passages 32, 34 which communicate, respectively, with the supply line 22 and drain line 24. The face sealing valve member 26 is provided with an arcuate channel 36 which, in the position illustrated in Figure 2, provides a communication path between the first passage 32 and a common passage (not shown) which, in use, communicates with the chamber 18. In the position illustrated in Figure 2, the second passage 34 is closed by the valve member 26. From the position illustrated in Figure 2, rotation of the valve member 26 about its axis of rotation 38 breaks the communication between the channel 36 and the first passage 32, closing the first passage, and instead opens communication between the channel 36 and the second passage 34, allowing fluid to flow from the chamber 18 to the drain line 24.

In order to drive the rotary valve member 26 for rotation about the axis of rotation 38, the rotary valve member 26 is mounted upon a drive shaft 40 which, in turn, is rigidly connected to a rocker arm 42, the drive shaft 40 and rocker arm 42 both being rotatable or pivotable about the axis 38. Bearings (not shown) are provided to support the drive shaft 40 for angular movement, the bearings including a thrust bearing arranged to carry the axial load on the drive shaft 40 resulting from the action ofthe pressurised fluid on the valve member 26 from the first passage 32.

An electromagnetic actuator arrangement 46 is provided to cause angular movement of the rocker member 42 to take place, in use. The actuator arrangement 46 could take a range of forms, for example it could take substantially the form illustrated in Figure 3 in which a magnetic core 48 carries a pair of pole pieces 50, the core 48 having permanent magnets 52 mounted therein and having a coil 54 mounted thereon. The rocker member 42 is supported by the drive shaft 40 so as to be located between the pole pieces 50. A relatively light spring 56 is provided to hold the rocker member 42 in either of its extreme positions when actuation is not taking place.

In use, with the actuator valve in the position illustrated in the drawings, and with the coil 54 de-energised, the rocker member 42 occupies one of its stable conditions and is held against angular movement by the spring 56. In this position, the valve member 26 is orientated to allow communication between the supply line 22 and the chamber 18, thus drilling fluid under pressure is supplied to the chamber 18 urging the associated pad 12 towards its extended position. From this position, energisation ofthe coil 54 causes the rocker member 42 to move angularly about the axis of rotation 38 to its opposite stable position. Once this position has been attained, the coil 54 can be de-energised, the spring 56 holding the rocker member 42 in this position. The movement of the rocker member 42 is transmitted by the drive shaft 40 to the valve member 26, rotating the valve member 26 to break communication between the supply line 22 and the chamber 18, instead opening communication between the chamber 18 and the drain line 24, thereby allowing a reduction in the fluid pressure within the chamber 18, enabling the associated pad 12 to move to its retracted position.

Energisation of the coil 54 with the opposite polarity will cause the rocker member 42 to return to the position illustrated, with the result that the chamber 18 is again charged with fluid under pressure. Again, once this position of the rocker member 42 is attained, the coil 54 can be de-energised, the spring 56 holding the rocker member 42 in this stable condition.

As the load on the rocker member 42 caused by the application of fluid under pressure is borne by the bearings, and in any event acts in the direction ofthe axis of rotation 38, the spring force required to hold the rocker member 42 in its stable positions, in use, can be relatively light.

The actuator arrangement 46 is housed within a housing 58 which isolates the actuator arrangement 46 from the drilling fluid, thereby reducing the risk of damage to the actuator arrangement 46 caused by the pressure of the fluid, the temperature thereof, or the corrosive effects ofthe fluid. If desired, the housing 58 maybe filled with a non-corrosive, clean fluid.

There is a risk, with bi-stable actuator valves, of the control unit used to control the operation ofthe valves losing track ofthe current status ofthe valves, for example if there is a power supply failure or the valves fail to switch when a switching signal is applied thereto. In order to overcome this potential disadvantage, a position sensor 70 may be provided to monitor the position occupied by the valve member 26. The sensor 70 may be a contact sensor, for example in the form of a microswitch or the like. Alternatively, it may comprise a non-contact sensor, for example in the form of a Hall effect sensor monitoring the position of a magnet mounted upon or movable with the valve member 26. Rather than monitor the position of the valve member 26 directly, the excitation of the coil 54 may be monitored. By monitoring the electrical load on the coil 54, in particular looking for changes in the load, an indication can be determined of whether the rocker member 42 has moved in response to the excitation of the coil 54.

Figure 4 illustrates part of an alternative actuator arrangement. As illustrated in Figure 4, the actuator arrangement includes an excitation coil 60 located around part of a core 62. In order to protect the coil 60 from the pressurised drilling fluid, which may be at high temperature and is potentially corrosive, the coil 60 is located within a protective housing 64. In order to minimise the spacing of the coil 60 from the core 62, and hence minimise the magnetic disturbance caused by the presence of the housing 64, the housing 64 is of thin walled form. However, in order to withstand the pressure of the drilling fluid, in use, the housing 64 must be of a strong material and in the arrangement illustrated is of stainless steel form. As not only the coil 60 must be protected from the drilling fluid, but also other parts of the electrical circuit to which the coil 60 is connected should ideally be protected, the housing 64 also houses, for example, the wires 66 and bulkhead connector 68 to which the coil is connected.

Although the description hereinbefore is of specific arrangements, it will be appreciated that a range of modifications or alterations may be made thereto within the scope of the invention.

Claims (28)

1. A bias unit comprising a plurality of actuators, each being operable under the application of fluid under pressure thereto to move an associated bias pad from a retracted position to an extended position, and a plurality of actuator valves arranged to control the supply of fluid under pressure to the actuators, wherein at least one of the actuator valves is an electrically controllable bi-stable valve.

2. A bias unit according to Claim 1, wherein the or each bi-stable valve is solenoid actuated.

3. A bias unit according to Claim 2, wherein the or each bi-stable valve includes an excitation coil which is provided within a protective housing.

4. A bias unit according to Claim 3, wherein the housing further contains wires and/or connectors connected to the excitation coil.

5. A bias unit according to any one of Claims 3 and 4, wherein the housing is of thin walled construction.

6. A bias unit according to Claim 5, wherein the housing is of stainless steel.

7. A bias unit according to any one ofthe preceding claims, further comprising a position sensor arranged to monitor the position occupied by a valve member of the actuator valve.

8. A bias unit according to Claim 7, wherein the position sensor is a contact sensor.

9. A bias unit according to Claim 8, wherein the contact sensor comprises a microswitch.

10. A bias unit according to Claim 7, wherein the position sensor comprises a non-contact sensor.

11. A bias unit according to Claim 10, wherein the sensor comprises a Hall effect sensor.

12. A bias unit according to any one of Claims 1 to 6, further comprising a sensor arranged to monitor the operation of an excitation coil of the actuator valve.

13. A bias unit according to any one ofthe preceding claims, wherein the or each bi-stable actuator valve includes a rotary face sealing valve.

14. A bias unit according to Claim 13, wherein the rotary face sealing valve includes a rotary valve member connected to a rocker member moveable between stable conditions by an electromagnetic actuator.

15. A bias unit according to Claim 14, further comprising a spring to hold the rocker member in its stable conditions.

16. An electrically controllable bi-stable valve suitable for use in the bias unit of any one of Claims 1 to 15 to control the supply of fluid under pressure to at least one of the actuators thereof.

17. A valve according to Claim 16, comprising a face sealing valve member rotatable about an axis between a first position in which communication is permitted between an inlet and a first outlet, a second outlet being closed, and a second position in which the first outlet is closed and communication is permitted between the inlet and the second outlet.

18. A valve according to Claim 16 or Claim 17, further comprising an excitation coil, a housing being provided to protect the coil from damage due to the environment in which it is intended to operate.

19. A valve according to Claim 18, wherein the housing is ofthin-walled form.

20. A valve according to Claim 19, wherein the housing is of stainless steel.

21. A valve according to any one of Claims 16 to 20, further comprising a sensor to allow the state of the valve to be sensed.

22. A valve according to Claim 21, wherein the sensor comprises a contact sensor.

23. A valve according to Claim 22, wherein the sensor comprises a microswitch.

24. A valve according to Claim 21, wherein the sensor comprises a noncontact sensor.

25. A valve according to Claim 24, wherein the sensor comprises a Hall effect

A 1'

sensor.

26. A valve according to Claim 21, wherein the sensor is arranged to monitor the operation of an excitation coil of the valve to provide an indication of the position occupied by the valve or switching thereof.

27. A bias unit substantially as hereinbefore described with reference to the accompanying drawings.

28. An actuator valve substantially as hereinbefore described with reference to the accompanying drawings.