Valve for a downhole tool

A commutating valve for a downhole steering tool. The downhole steering tool has a sleeve which surrounds an annular body which in turn surrounds a driveshaft. A plurality of steering cylinders are located in the annular body and a steering piston is located in each steering cylinder, the steering pistons engaging the sleeve. A pump pressurizes hydraulic fluid within a reservoir, the reservoir having a closable outlet whereby the pressure of the hydraulic fluid within the reservoir can be raised by closing the outlet and lowered by opening the outlet. The valve comprises a number of discrete valve members which are all in communication with the reservoir and can be opened sequentially whereby to deliver hydraulic fluid to the steering cylinders sequentially. The pressure within each steering cylinder can be controlled in order to control the position of the driveshaft within the sleeve.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority to United Kingdom Patent Application No. GB1114286.6 filed Aug. 19, 2011, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to valve for a downhole tool, and in particular to a commutating valve for use in a downhole steering tool such as that of EP 1 024 245.

BACKGROUND OF THE INVENTION

A downhole steering tool (or “controllable stabiliser”) is described in EP 1 024 245. As indicated in that document, the steering tool is used to control the drilling direction by forcing a part of the driveshaft away from the longitudinal centreline of the borehole, thereby forcing the drill bit to deviate from a linear path.

The steering tool comprises a number of steering pistons located in respective steering cylinders spaced around the circumference of the steering tool, the steering cylinders being individually pressurised whereby the steering pistons to opposed sides of the steering tool can project from their steering cylinders by differing and controllable distances. The pressure of the fluid within each steering cylinder, and therefore the projection of each steering piston, is controlled by a commutating valve which delivers hydraulic fluid to each of the steering cylinders in turn, the pressure delivered to each steering cylinder being determined in accordance with the desired steering piston projection.

The present invention relates to a valve which is designed primarily to replace the commutating valve described in EP 1 024 245 The teaching of that document is incorporated into this document by reference so as to avoid the unnecessary repetition of much of the common componentry and method of operation. Whilst much of the following description therefore relates to the invention incorporated as a commutating valve in a downhole steering tool, it will be understood that the invention could be used on other downhole applications.

FIG. 4 of EP 1 024 245 is reproduced asFIG. 1herein for ease of reference. The steering tool (16) surrounds a part of the driveshaft (12). The driveshaft (12) is connected to the drill string and the drill bit, neither of which is shown inFIG. 1, in known fashion. The steering tool (16) comprises a body (48) and a sleeve (58), the body (48) and sleeve (58) being separated by a fluid-filled annulus (56). Formed in the body (48) are six steering cylinders (50), each of which carries a steering piston (52), only one of the steering cylinders and steering pistons being shown inFIG. 1(the other five steering cylinders and steering pistons are identical to the steering cylinder and steering piston shown inFIG. 1, and spaced at 60° intervals around the body (48)). In use, the driveshaft (12) will rotate and the body (48) will be substantially non-rotating, i.e. the body (48) will be held substantially rotationally stationary by the engagement of the sleeve (58) with the surrounding borehole wall. Whilst an arrangement having six steering cylinders (50) is described in EP 1 024 245, practical embodiments of that invention have twelve steering cylinders spaced at 30° intervals around the body. It will be understood that the present invention can be used with any number of steering cylinders.

The steering tool (16) has an annular reservoir of pressurised hydraulic fluid which is not seen inFIG. 1, the reservoir being connected to a channel (26) located in an annular commutating valve (24). Importantly, the commutating valve (24) is fixed to rotate with the driveshaft (12) and therefore rotates relative to the body (48), so that as the driveshaft (12) and commutating valve (24) rotate the channel (26) periodically communicates with each of the steering cylinders (50) by way of its respective conduit (54).

A solenoid valve (not seen inFIG. 1) can be opened to relieve the pressure within the channel (26). As long as the solenoid valve remains open all of the steering cylinders (50) experience the same pressure and the body (48) (and therefore the driveshaft (12)) remains centrally located relative to the sleeve (58) and borehole. To cause the driveshaft (12) to move away from its central location the solenoid valve is closed whilst the channel (26) is in communication with a chosen steering cylinder (50), that steering cylinder receiving higher-pressure hydraulic fluid which causes the respective piston (52) to be driven outwardly.

It is essential to the correct operation of the commutating valve (24) that the higher-pressure hydraulic fluid is only delivered to the chosen steering cylinder (or chosen adjacent steering cylinders), and this requires a fluid-tight seal to be present between the commutating valve (24) and the body (48). The seal between these components, both inFIG. 1and in practical embodiments of the steering tool, is provided by the accurate machining of the sliding metal surfaces.

In practice, the steering tool (16) experiences significant temperature variations in use, and the thermal expansion of the commutating valve (24) and body (48) prevent the maintenance of a perfect seal. In practical embodiments the adverse effects of the less than perfect seal are sought to be overcome by using a more viscous hydraulic fluid. However, there is a limit to the viscosity which can be used since the solenoid valve must operate with the hydraulic fluid, and if the hydraulic fluid is too viscous the solenoid valve will not be able to close. Whilst a spring can be used to assist closure of the solenoid valve the force provided by the spring must be somewhat less than the electromotive (valve opening) force which can be provided by the solenoid, so that in practice a strong spring cannot be used to assist valve closure.

Also, a given steering tool is likely to have to operate in different temperature regimes, i.e. the temperature varies according to the depth and location of the borehole in which the steering tool is being used, and a high viscosity hydraulic fluid suitable for use in a high temperature borehole might be too viscous in a low temperature borehole, resulting in significant pumping losses and perhaps leading to tool failure in the event that the solenoid valve cannot close. Alternatively, a low viscosity hydraulic fluid suitable for a low temperature borehole is likely to leak between the commutating valve (24) and the body (48) when used in a high temperature borehole, again perhaps leading to tool failure.

SUMMARY OF THE INVENTION

Despite the significant benefits of the steering tool of EP 1 024 245, the inventor has realised that there is a need for an improved valve for use as a commutating valve which reduces the likelihood of tool failure and therefore increases the applicability of the steering tool, and allows its use across a wider range of temperatures. An object of the present invention is therefore to provide a valve which is less vulnerable to leakage. Such a valve can be used with a less viscous hydraulic fluid, enabling a reduction in pumping losses, the use of a lower powered solenoid valve, the use of less robust componentry, and can result in a longer expected working life for the solenoid valve and other componentry.

According to the invention, there is provided a valve for a downhole tool, the valve comprising a plurality of discrete valve members and an actuator, the actuator being adapted to open the valve members sequentially. The valve therefore comprises an assembly of discrete valve members, and can be configured as a commutating valve.

The single sliding seal between the valve (24) and the body (48) in the commutating valve of EP 1 024 245 is therefore replaced by a number of discrete valve members, each valve member being able to vary the rate of flow of hydraulic fluid. Ideally, each valve member is able to permit or prevent the passage of hydraulic fluid, i.e. each valve member has an “open” and a “closed” condition.

Whilst the valve has been designed for use primarily with a steering tool, and in particular the steering tool of EP 1 024 245, it is not limited to that tool and may be used in other steering tools utilising a commutating valve, as well as in other valve applications as indicated above.

Preferably, each valve member is a ball locatable upon a seat. Ball valves are known to be very reliable and substantially leak-free, and are suited to two-position (open or closed) operation.

Desirably, the valve member is engaged by a valve piston, the valve piston being movable within a valve cylinder it is desirably arranged that the valve piston engages the valve member and can drive the valve member to its closed position.

Preferably, the valve cylinder, at its end opposed to the valve member, has an inlet for hydraulic fluid. It can thereby be arranged that hydraulic fluid, at substantially the same pressure, is delivered to both sides of the valve piston when the valve member is open. The force exerted by the hydraulic fluid can therefore be balanced to both sides of the valve piston, permitting the valve piston to be moved to close the valve member by a relatively small closing force. The closing force is ideally provided by a resilient biasing means, ideally a compression spring.

Desirably, the actuator communicates with the valve member by way of a movable plunger, the plunger being movable in a bore within the body of the tool. The bore preferably terminates at the valve seat. Desirably, the bore has at least one inlet for hydraulic fluid. When the valve member is open the hydraulic fluid can flow from the bore, past the valve member and into the valve cylinder below the valve piston.

In use as a commutating valve of a steering tool such as EP 1 024 245, each valve cylinder of the commutating valve has an outlet at its end adjacent to the valve member, the outlet communicating hydraulic fluid to an individual steering cylinder (50). Accordingly, when the solenoid valve is closed pressurised hydraulic fluid can be delivered through a chosen commutating valve cylinder to a chosen steering cylinder (50).

There is also provided a steering tool for a drillstring, the steering tool having an annular body adapted to surround a part of the drillstring and a sleeve adapted to surround the body, the steering tool having a plurality of steering cylinders formed in the body and a respective steering piston located in each steering cylinder, the steering tool carrying a volume of hydraulic fluid and having a hydraulic pump adapted to pump hydraulic fluid into a reservoir, the reservoir having a closable outlet whereby the pressure within the reservoir can be raised when the outlet is closed and lowered when the outlet is opened, a commutating valve in communication with the reservoir and adapted to deliver hydraulic fluid to the steering cylinders sequentially, the commutating valve comprising a number of discrete valve members and an actuator, the actuator being adapted to open the valve members sequentially.

Preferably the reservoir outlet is closed by a solenoid valve.

DETAILED DESCRIPTION OF DRAWINGS

A description of the relevant parts of the prior art arrangement ofFIG. 1is set out above and will not be repeated.

The valve assembly or commutating valve124ofFIGS. 2 and 3, and the valve assembly or commutating valve224ofFIG. 4, have been designed to replace the commutating valve24and channel26of the steering tool described in EP 1 024 245, and thereby provide an alternative means of delivering pressurised hydraulic fluid to the steering cylinders50. As with the commutating valve24described in EP 1 024 245, the commutating valve124,224is adapted to interconnect a reservoir146of hydraulic fluid (see also the reservoir246ofFIG. 4) with the respective steering cylinders50once for each rotation of the drill string12.

The pressure of the hydraulic fluid within the reservoir can be varied, preferably by way of a pump (see the pump38ofFIG. 4) which pumps hydraulic fluid into the reservoir146,246and a solenoid valve32which can allow the escape of hydraulic fluid from the reservoir by way of a closable outlet30. As in EP 1 024 245 the pump38is operated continuously and the solenoid valve32is operated intermittently, the pump and solenoid valve together determining the pressure of the hydraulic fluid which is communicated to the steering cylinders50. If the solenoid valve32is open the hydraulic fluid within the reservoir146,246is at a low pressure and if the solenoid valve32is closed the hydraulic fluid within the reservoir is at a high pressure. Whilst alternative means for selectively varying the pressure of the hydraulic fluid can be provided, and can be used with the present invention, it is preferred to use a similar arrangement to that described in EP 1 024 245, as is shown inFIG. 4.

The delivery of high pressure hydraulic fluid to a particular steering cylinder50(or to particular adjacent steering cylinders) causes the respective piston(s)52to be moved outwardly in order to deviate the driveshaft12, as described above.

As is common in downhole steering tools, the steering componentry is located within a chamber which is filled with hydraulic fluid. In known fashion, the pressure of the hydraulic fluid within the tool is firstly matched (for example by way of a pressure-balancing piston) to that of the surrounding borehole whereby to minimise the likelihood of leaks. Secondly, a hydraulic pump38is provided whereby to raise the pressure of the hydraulic fluid in certain (high pressure) parts of the tool. The hydraulic pump of the embodiment ofFIGS. 2 and 3may be similar to that shown inFIG. 4, which is itself similar to that of FIG. 3 of EP 1 024 245 and referred to by the numeral38. In EP 1 024 245 the hydraulic pump can raise the pressure of the hydraulic fluid within the reservoir and the channel26whenever the solenoid valve is closed. When the solenoid valve32is opened the pressure within the reservoir146,246and channel26is relieved to a pressure substantially the same as the (lower) pressure within the remainder of the tool. The solenoid valve therefore determines whether the reservoir contains hydraulic fluid at a relatively high pressure or at a relatively low pressure, the actual pressures being determined by the conditions of use.

The commutating valve124ofFIGS. 2 and 3utilises a reservoir146. As above described, the pressure of the hydraulic fluid within the reservoir146is preferably controlled by a pump and solenoid valve similar to those ofFIG. 4and EP 1 024 245. It will be understood that the pump (not shown inFIG. 2 or 3) acts continuously to increase the pressure within the reservoir146, whilst the solenoid valve (also not shown inFIG. 2 or 3) acts intermittently to permit or prevent the escape of hydraulic fluid from the reservoir146. It is arranged that the open solenoid valve can permit hydraulic fluid to flow out of the reservoir146at a greater rate than it is being introduced by the pump, so that when the solenoid valve is open the pressure within the reservoir is reduced to substantially that of the surrounding borehole.

The steering tool includes an actuator, in this embodiment a rotary actuator114which is connected directly to the driveshaft (not shown inFIG. 2 or 3, but see the driveshaft212ofFIG. 4) and rotates with the driveshaft. As shown inFIG. 3, the actuator114includes a first cammed section116, a large-diameter section118, a second cammed section120and a small-diameter section122. The small-diameter section122runs from the second cammed section120to the first cammed section116so that there is only a single large-diameter section118upon the circumference of the actuator114.

The actuator114engages a plunger130. The plunger130is mounted within a bore132of an insert134which is fixed into a drilled opening136in the body148of the tool. The body148does not rotate with the driveshaft so that the actuator114rotates relative to the plunger130. As the actuator114rotates (clockwise as drawn inFIG. 3), once in each revolution the plunger130will engage the first cammed section116and the large-diameter section118and the plunger will be moved (upwards as drawn) from the position shown.

The end of the plunger130opposed to the actuator114engages a ball138. Whilst the plunger130is in engagement with the small-diameter section122of the actuator114the ball138rests upon its seat140; however, when the plunger130is moved by the first cammed section116the ball138is lifted from its seat140. The ball138is held away from its seat140by the plunger130whilst the plunger engages the large-diameter section118of the actuator114, so that the circumferential length of the large-diameter section118determines the duration for which the valve member138,140is held open.

Only one valve member138,140is shown inFIGS. 2 and 3, but (similarly toFIG. 1) it will be understood that there is a plurality of valve members in the commutating valve124(one for each of the steering cylinders50) located circumferentially around the body148. In embodiments having six steering cylinders50the commutating valve124has six valve members138,140spaced at approximately 60° intervals around the body148, and the first cammed section116and the large-diameter section118will engage the plunger130of each of the valve members sequentially.

Importantly, the combined circumferential length of the first cammed section116, the raised section118and the second cammed section120is no greater than (and is preferably less than) the distance between the plungers130of adjacent valve members138,140, so that each valve member is closed before the next valve member is opened. Accordingly, only one of the valve members138,140is open at a time, so that hydraulic fluid can be delivered to individual steering cylinders50as desired.

Regardless of the pressure of the hydraulic fluid within the reservoir146, each of the valves members138,140will therefore open once for each revolution of the driveshaft12and actuator114.

The drilled opening136includes a second insert142which defines a valve cylinder144and carries a movable valve piston160. The valve piston160engages the ball138and is therefore moved (upwardly as drawn) from the position shown inFIGS. 2 and 3as the ball138is lifted from its seat140. The valve piston160is biased towards the (valve closed) position by a compression spring162, so that the compression spring162serves to close the valve member138,140.

The body148has conduits formed therethrough for communicating hydraulic fluid to and from the commutating valve124. A first set of conduits164,166connect the reservoir146to passageways168within the first insert134, the first set of conduits164,166and the passageways168thereby permitting hydraulic fluid to enter the bore132underneath the valve seat140. It will be understood that whilstFIG. 3does not show any clearance around the plunger130, clearance for the passage of hydraulic fluid is provided above the passageways168.

A branch170off the conduit166, and passageways172through the second insert142, connect the reservoir146with the cylinder144above the valve piston160(i.e. to the side of the valve piston160opposed to the ball138).

A second conduit154communicates with the drilled opening136between the first insert134and the second insert142, so that the second conduit is connected to the outlet of the valve member138,140. Accordingly, when the ball138is lifted from its seat140, hydraulic fluid is communicated from the passageways168, along the bore132around the plunger130, past the ball138and into the second conduit154. It will be understood that the second conduit154delivers hydraulic fluid to a particular steering cylinder50, so that when the valve member138,140is open the reservoir146is connected to the steering cylinder50of that valve member. In the event that the solenoid valve is closed and the pressure within the reservoir146is at the higher pressure, the steering piston52will be driven outwardly to deviate the drillstring.

It will be understood that when the valve member138,140is open, substantially the same hydraulic pressure acts to both sides of the valve piston160, regardless of the actual pressure within the reservoir146. Since the areas of each side of the valve piston160are the same, the hydraulic forces acting upon the valve piston are balanced. As soon as the plunger130passes the second cammed section120of the actuator114and is no longer holding the ball138off its seat140, the spring162can drive the ball138onto its seat140whereby to close the valve member.

It will also be understood that the area of the valve piston160is greater than the area of the bore132, so that, when the valve member138,140is closed the hydraulic force upon the valve piston is greater than the hydraulic force upon the ball140, holding the valve member shut.

It will be appreciated that there is only a small radial distance between the driveshaft12and the periphery of the body148in which to locate the commutating valve124, but because of the balanced hydraulic forces upon the valve piston160the spring162does not need to be large and a suitable spring can be fitted into the space available.

In the alternative embodiment ofFIG. 4, the valve members238,240are located longitudinally rather than radially, but the operation of the commutating valve224, and the operation of the steering tool, are similar. Accordingly, in the embodiment ofFIG. 4the plunger230and the ball238move parallel to the longitudinal axis A-A of the steering tool, rather than perpendicular to the longitudinal axis as in the embodiment ofFIGS. 2 and 3.

Again, only one of the valve members238,240is shown inFIG. 4, but it will be understood that the commutating valve224comprises a plurality of valve members spaced circumferentially around the body248of the steering tool, with one valve member238,240for each steering cylinder50.

The steering tool ofFIG. 4has a rotary actuator214which is connected directly to the driveshaft212and rotates with the driveshaft212. The actuator214includes a first sloping section216, a raised section218, a second sloping section220and a planar section222. The planar section222runs from the second sloping section220to the first sloping section216so that there is only a single raised section218upon the surface of the actuator214.

As the actuator214rotates around the longitudinal axis A-A, it moves past the plunger230in a downwards direction as drawn. The first sloping section216pushes the plunger230to the left as drawn, moving the ball238off its seat240. Hydraulic fluid is communicated from the reservoir246, along the first conduit264, through the passageways268and bore232, past the ball238and along the second conduit254to a respective steering cylinder50. The length of the raised section218determines the duration for which the valve member238,240is held open.

As in the embodiment ofFIGS. 2 and 3, the hydraulic forces acting upon the valve piston260are balanced by virtue of a conduit270which communicates hydraulic fluid from the reservoir246to the end of the cylinder244opposed to the ball238. Thus, notwithstanding that there is more (longitudinal) space available in this embodiment in which to locate the valve closing spring262, the force exerted by the spring262need not be large.

It will be understood that in the embodiment ofFIGS. 2 and 3, one drilled opening136, with its valve member138,140and other componentry, is provided for each of the steering cylinders50. In the event that the steering tool has six steering cylinders50, it is expected that there is sufficient room within the body148to locate six drilled openings136in the same plane (at 60° intervals around the body148). If, however, there are more steering cylinders50, for example twelve steering cylinders, there may not be sufficient room to locate twelve drilled openings136in the same longitudinal plane. In such a case, the commutating valve124can comprise two (or more) banks of drilled openings136, the respective banks being separated along the longitudinal axis A-A of the steering tool. There may for example be six drilled openings136lying in a first plane at one longitudinal position, and six drilled openings136lying in a second plane at another longitudinal position, the respective drilled openings in the first plane preferably being offset from those in the second plane (for example by 30°) so as to facilitate communication of hydraulic fluid to and from all of the drilled openings136.

Similarly, for the valve member shown inFIG. 4, it is not necessary that all of the valve members238,240be arranged at the same radius if space is a concern. For example, four valve members238,240could be located at a first radial distance (close to the driveshaft), and eight valve members238,240could be located at a second radial distance (farther from the driveshaft). The rotary actuator214could have a first raised section at the first radial distance and a second raised section at the second radial distance. Despite their location at different radial positions, it would preferably be arranged that the valve members lie at 30° intervals around the body248. Also, the length of the first raised section should be shorter than the length of the second raised section so that all of the respective valves238,240are held open for the same period of time.

The cammed portions116and120ofFIG. 3, and the sloping portions216and220ofFIG. 4, are shown to be substantially linear, but they can be curved if desired (and rounded where they meet the adjacent actuator portions). The inclination of the first cammed portion116is smaller than the inclination of the second cammed portion120(and similarly for the first and second sloping portions216,220) so that the rate at which the plunger130,230is moved to open the valve member is slower than the rate of movement to close the valve member.

It will be understood that the inclination of the second cammed portion120, and the inclination of the second sloping portion220, may exceed the rate at which the valve member can close, i.e. the inclination may exceed the rate at which the respective spring162,262can force the ball138,238against its seat140,240, in which case the plunger may be temporarily disengaged from the actuator. It is desired, however, that the angle of inclination of the second cammed portion120, and the angle of inclination of the second sloping portion220, are sufficiently shallow to maintain the engagement between the respective plunger130,230and its actuator114,214.

The use of separate valve members, and in particular ball valves, enables the use of lower viscosity hydraulic fluid than is typically used in a steering tool of EP 1 024 245, even in higher temperature boreholes. The use of a lower viscosity hydraulic fluid in turn leads to reduced pumping losses, enables the use of a lower powered solenoid valve and results in a longer expected working life for the solenoid valve.