Patent Application
20130043032
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.
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.
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 as
The steering tool (16) has an annular reservoir of pressurised hydraulic fluid which is not seen in
A solenoid valve (not seen in
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 in
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.
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.
The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:
A description of the relevant parts of the prior art arrangement of
The valve assembly or commutating valve 124 of
The pressure of the hydraulic fluid within the reservoir can be varied, preferably by way of a pump which pumps hydraulic fluid into the reservoir and a solenoid valve which can allow the escape of hydraulic fluid from the reservoir. In EP 1 024 245 the pump is operated continuously and the solenoid valve is operated intermittently, the pump and solenoid valve together determining the pressure of the hydraulic fluid which is communicated to the steering cylinders 50. If the solenoid valve is open the hydraulic fluid within the reservoir is at a low pressure and if the solenoid valve is 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.
The delivery of high pressure hydraulic fluid to a particular steering cylinder 50 (or to particular adjacent steering cylinders) causes the respective piston(s) 52 to be moved outwardly in order to deviate the driveshaft 12, 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 pump (not shown) is provided whereby to raise the pressure of the hydraulic fluid in certain (high pressure) parts of the tool. The hydraulic pump may be similar to that shown in FIG. 3 of EP 1 024 245 and referred to by the numeral 38. In EP 1 024 245 the hydraulic pump can raise the pressure of the hydraulic fluid within the reservoir and the channel 26 whenever the solenoid valve is closed. When the solenoid valve is opened the pressure within the reservoir and channel 26 is 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 valve 124 of
The steering tool includes an actuator, in this embodiment a rotary actuator 114 which is connected directly to the driveshaft (not shown) and rotates with the driveshaft. As shown in
The actuator 114 engages a plunger 130. The plunger 130 is mounted within a bore 132 of an insert 134 which is fixed into a drilled opening 136 in the body 148 of the tool. The body 148 does not rotate with the driveshaft so that the actuator 114 rotates relative to the plunger 130. As the actuator 114 rotates (clockwise as drawn in
The end of the plunger 130 opposed to the actuator 114 engages a ball 138. Whilst the plunger 130 is in engagement with the small-diameter section 122 of the actuator 114 the ball 138 rests upon its seat 140; however, when the plunger 130 is moved by the first cammed section 116 the ball 138 is lifted from its seat 140. The ball 138 is held away from its seat 140 by the plunger 130 whilst the plunger engages the large-diameter section 118 of the actuator 114, so that the circumferential length of the large-diameter section 118 determines the duration for which the valve member 138, 140 is held open.
Only one valve member 138, 140 is shown in
Importantly, the combined circumferential length of the first cammed section 116, the raised section 118 and the second cammed section 120 is no greater than (and is preferably less than) the distance between the plungers 130 of adjacent valve members 138, 140, so that each valve member is closed before the next valve member is opened. Accordingly, only one of the valve members 138, 140 is open at a time, so that hydraulic fluid can be delivered to individual steering cylinders 50 as desired.
Regardless of the pressure of the hydraulic fluid within the reservoir 146, each of the valves members 138, 140 will therefore open once for each revolution of the driveshaft 12 and actuator 114.
The drilled opening 136 includes a second insert 142 which defines a valve cylinder 144 and carries a movable valve piston 160. The valve piston 160 engages the ball 138 and is therefore moved (upwardly as drawn) from the position shown in
The body 148 has conduits formed therethrough for communicating hydraulic fluid to and from the commutating valve 124. A first set of conduits 164, 166 connect the reservoir 146 to passageways 168 within the first insert 134, the first set of conduits 164, 166 and the passageways 168 thereby permitting hydraulic fluid to enter the bore 132 underneath the valve seat 140. It will be understood that whilst
A branch 170 off the conduit 166, and passageways 172 through the second insert 142, connect the reservoir 146 with the cylinder 144 above the valve piston 160 (i.e. to the side of the valve piston 160 opposed to the ball 138).
A second conduit 154 communicates with the drilled opening 136 between the first insert 134 and the second insert 142, so that the second conduit is connected to the outlet of the valve member 138, 140. Accordingly, when the ball 138 is lifted from its seat 140, hydraulic fluid is communicated from the passageways 168, along the bore 132 around the plunger 130, past the ball 138 and into the second conduit 154. It will be understood that the second conduit 154 delivers hydraulic fluid to a particular steering cylinder 50, so that when the valve member 138, 140 is open the reservoir 146 is connected to the steering cylinder 50 of that valve member. In the event that the solenoid valve is closed and the pressure within the reservoir 146 is at the higher pressure, the steering piston 52 will be driven outwardly to deviate the drillstring 12.
It will be understood that when the valve member 138, 140 is open, substantially the same hydraulic pressure acts to both sides of the valve piston 160, regardless of the actual pressure within the reservoir 146. Since the areas of each side of the valve piston 160 are the same, the hydraulic forces acting upon the valve piston are balanced. As soon as the plunger 130 passes the second cammed section 120 of the actuator 114 and is no longer holding the ball 138 off its seat 140, the spring 162 can drive the ball 138 onto its seat 140 whereby to close the valve member.
It will also be understood that the area of the valve piston 160 is greater than the area of the bore 132, so that, when the valve member 138, 140 is closed the hydraulic force upon the valve piston is greater than the hydraulic force upon the ball 140, holding the valve member shut.
It will be appreciated that there is only a small radial distance between the driveshaft 12 and the periphery of the body 148 in which to locate the commutating valve 124, but because of the balanced hydraulic forces upon the valve piston 160 the spring 162 does not need to be large and a suitable spring can be fitted into the space available.
In the alternative embodiment of
Again, only one of the valve members 238, 240 is shown in
The steering tool of
As the actuator 214 rotates around the longitudinal axis A-A, it moves past the plunger 230 in a downwards direction as drawn. The first sloping section 216 pushes the plunger 230 to the left as drawn, moving the ball 238 off its seat 240. Hydraulic fluid is communicated from the reservoir 246, along the first conduit 264, through the passageways 268 and bore 232, past the ball 238 and along the second conduit 254 to a respective steering cylinder 50. The length of the raised section 218 determines the duration for which the valve member 238, 240 is held open.
As in the embodiment of
It will be understood that in the embodiment of
Similarly, for the valve member shown in
The cammed portions 116 and 120 of
It will be understood that the inclination of the second cammed portion 120, and the inclination of the second sloping portion 220, may exceed the rate at which the valve member can close, i.e. the inclination may exceed the rate at which the respective spring 162, 262 can force the ball 138, 238 against its seat 140, 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 portion 120, and the angle of inclination of the second sloping portion 220, are sufficiently shallow to maintain the engagement between the respective plunger 130, 230 and its actuator 114, 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1114286.6 | Aug 2011 | GB | national |
