WO2012168705A2

WO2012168705A2 - Valve control device

Info

Publication number: WO2012168705A2
Application number: PCT/GB2012/051270
Authority: WO
Inventors: Martin George BRUCE
Original assignee: Mgb Oilfield Services Limited
Priority date: 2011-06-06
Filing date: 2012-06-06
Publication date: 2012-12-13
Also published as: GB201109428D0; WO2012168705A3

Abstract

A valve device disclosed for use in an oil or gas well, in order to actuate a valve between closed and open configurations. The valve device has a bore with a piston member axially moveable in the bore between first and second configurations. The piston is urged to move axially between the first and the second configurations within the bore by fluid pressure applied to the piston, and the axial movement of the piston from the first to the second configuration under the force of the fluid pressure is opposed by the force of a spring device. The piston is urged by a magnetic force to move axially from the first to the second configuration in the same direction as the force applied by the fluid pressure, and against the force of the spring device. The magnetic force applied to the piston when the piston is in the first configuration is less than the magnetic force applied to the piston when the piston is in the second configuration, so that as the piston approaches the second configuration under the force of the fluid pressure, the magnetic force increases as the piston moves under the force of the fluid pressure, whereby the magnetic force and the fluid pressure together overcome the force of the spring device to move the piston into the second configuration.

Description

VALVE CONTROL DEVICE

This invention relates to a valve control device, typically for activating or de- activating a valve that controls the flow of fluid in a downhole tool suitable for use in a wellbore.

Downhole valves are frequently used in oil and gas wells to divert fluid flow by opening or closing ports in a string in order to divert the flow of e.g. drilling fluid in a particular direction. For example, one typical application of a downhole valve is a circulation device used for drilling or in wellbore cleaning, in which the fluid normally flows down through the string when the valve is closed, exits from the bottom of the string or through the drill bit, and flows back up the annulus between the string and the wellbore in order to wash cuttings on other debris back to the surface. In long reach wells, it is common practice to circulate drilling fluid not just from the bottom hole assembly and drill bit, but also at various points along the drill string, and for that purpose, circulation subs have been devised that contain valves located some distance away from the bit, and arranged to be switched to divert the fluid from the inner bore of the drillstring out through the wall of the drillstring and into the annulus when the valve is open. This diverts the fluid into the annulus to wash cuttings back up to the surface without pumping the fluid all the way down the well to exit the string from the bottom hole assembly. Circulation subs such as these improve the circulation of drill fluid in the upper parts of the well, where reduced fluid pressures in the annular area can sometimes lead to settling of wellbore debris in the annulus, and inefficient washing back of the debris and cuttings back to the surface.

US2009/0020293 discloses a valve control device useful for understanding the invention. According to the invention, there is provided a valve control device having a bore with a piston member axially moveable in the bore between first and second configurations, wherein the piston is urged to move axially between the first and the second configurations within the bore by fluid pressure applied to the piston, and wherein the axial movement of the piston from the first to the second configuration under the force of the fluid pressure is opposed by the force of a spring device, wherein the piston is urged by a magnetic force to move axially from the first to the second configuration in the same direction as the force applied by the fluid pressure, and against the force of the spring device, and wherein the magnetic force applied to the piston when the piston is in the first configuration is less than the magnetic force applied to the piston when the piston is in the second configuration, whereby as the piston approaches the second configuration under the force of the fluid pressure, the magnetic force increases as the piston moves under the force of the fluid pressure, whereby the magnetic force and the fluid pressure together overcome the force of the spring device to move the piston into the second configuration.

Typically the magnetic force is an attractive force, attracting the piston to one end of the bore. Optionally the magnetic force can be a repellent force, acting to repel the piston away from an end of the bore. Typically the spring force is generated by a spring held in compression, acting to expand to push the piston away from one end of the bore. Optionally the spring force can be generated by a spring held in tension, acting to pull the piston towards one end of the bore. Typically, the force applied by the spring device is greater than the force applied by the magnet when the piston is in the second configuration. Accordingly, when the fluid pressure opposing the spring force is removed from the piston, the spring force is able to overcome the opposing magnetic force and return the piston to the first configuration under the force of the spring device. Typically, the fluid force and the magnetic force act in the same direction, and together oppose the force of the spring device.

Typically, when the piston is in the first configuration, the valve is closed, and fluid flowing through the bore of the valve is not diverted from the bore.

Typically, when the piston is in the second configuration, the valve is open and fluid flowing through the bore of the valve is diverted from the bore to another location, for example through a casing wall into an annular space between the casing and another tubular member of between the casing and the borehole.

Typically, the magnetic forces are applied by at least one magnet, typically by pair of magnets, one of which is disposed in the piston and is moveable in relation to the bore, and the other of which is disposed in a fixed location relative to the bore. More than one pair of magnets can be provided, and typically these can be aligned with one another so that the magnetic field on each one of each pair is arranged to attract the other of the pair when it moves within range. Optionally the piston does not need to carry a magnet; one of the magnets can be carried on a separate member such as a collar or sleeve that moves with the piston. Also, the body does not need to carry a magnet, one of the magnets can be carried on a separate member such as a collar or sleeve that moves with the body. As the piston moves so that the magnet on the piston comes within range of the fixed magnet associated with the bore, the magnetic force attracting the two magnets together increases in order to increase the motive force acting on the piston and overcome the force of the spring device to move the piston from the first configuration to the second configuration in conjunction with the force applied by the fluid pressure.

Using magnetic forces to assist the movement of the piston from the valve closed to the valve open configuration means that the valve can be provided with a strong spring force to reset it, but can be actuated with very small fluid pressures, and moving the valve from one configuration to the other does not require fluid pressure alone, but merely requires the fluid pressure to move the two magnets within range of one another in order to apply the magnetic force so that the combined force of the fluid pressure and the attractive force of the magnets together overcomes the opposing force of the spring device.

The magnets can be selected to be of appropriate strengths and to generate appropriate attractive forces so that the fluid pressure can be reduced to lower levels, allowing cost reduction and simplification in certain embodiments of the invention.

Initiation of the switching between the two configurations can also usefully be carried out by varying the fluid pressure alone, and the forces of the spring device and the magnets can typically be set when the tool is constructed. Setting the magnetic and spring forces so that the spring force is slightly larger than the magnetic force means that actuation of the device is possible simply by increasing the fluid pressure from the surface. It is generally easy to use existing surface pumps, etc. to pressure up the bore of a string from the surface, and so embodiments of the invention can utilise the existing architecture of a wellbore in order to operate embodiments of the invention. Also, actuation of the device simply by varying the force applied by the fluid pressure on the piston means that downhole signalling using electronics and other control lines is not required.

Typically, the piston is a tubular piston, and typically the bore passes through the piston. The piston can optionally be in the form of a sliding sleeve, which slides within a body through which the bore extends.

Typically, the piston can be keyed to a body to avoid rotation relative to the body.

Optionally, the piston can be locked in the first configuration, i.e. the closed configuration, by a shear pin or other locking device that retards the movement of the piston, and which can typically be overcome by fluid pressure rising above a threshold necessary to shear the pin.

Typically, the piston contains a flow restriction and typically has a differential piston area provided by first and second seals spaced axially along the piston, which define different surface areas, and which therefore cause the piston to move axially within the body in response to the application of fluid pressure to the piston.

Optionally, the piston can contain a ball catcher or similar device with a throat adapted to catch a ball or other device dropped into the string from the surface, whereby in the event of failure of the locking device, the device can be set to move the piston into the second configuration by dropping a ball into the ball catcher to be retained in the throat. Optionally the magnet associated with the piston can be carried on an end of the piston axially spaced from the spring. The magnet associated with the piston can optionally be carried on a sleeve that connects to the end of the piston, optionally by a screw thread. Optionally the sleeve bearing the magnet can have a bore that is concentric with the bore of the piston.

Optionally the magnet associated with the body can be carried on an end of the body axially spaced from the spring. The magnet associated with the body can optionally be carried on a sleeve that connects to the end of the body, optionally by a screw thread. Optionally the sleeve bearing the magnet can have a bore that is concentric with the bore of the body and optionally with the bore of the piston.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: -

Fig. 1 is a side sectional view of a valve device in a first closed configuration; Fig. 2 is a side sectional view of the Fig. 1 device in a second open configuration; Fig. 3 is a side sectional view of a second embodiment of a valve device in a first closed configuration;

Fig. 4 is a side sectional view of the Fig. 3 device in a second open configuration;

Fig. 5 is a side sectional view of a third embodiment of a valve device in a first closed configuration;

Fig. 6 is a side sectional view of the Fig. 5 device in a second open configuration; and

Fig 7 is a side sectional view of the Fig 5 and 6 embodiments in a reverse circulation configuration.

Referring now to Figs 1-2 of the drawings, a valve device is provided in the form of a circulation sub 10 having box and pin connection arrangements at opposite ends for connection of the sub 10 into a tubular string in an oil or gas well, such as a drillstring. The box 10b is located at the upper end closest to the surface, and the pin lOp is located at the lower end nearest to the drill bit. The sub 10 has a tubular body 11 with a central bore 12 extending axially through it. Between the box and pin sections, the central bore has an upper section 12u, a middle section 12m and a lower section 121. The upper section of the bore 12u adjacent to the box connection 10b at the portion of the sub 10 nearest to the surface has a wider inner diameter than the middle section 12m, which in turn has a wider inner diameter than the lower section 121, nearest to the pin connection at the lower end of the sub 10 nearest to the drill bit. Upwardly facing shoulder 13u is provided in the bore 12 between the upper and middle sections 12u, 12m, and upwardly facing shoulder 131 is provided at the inner diameter of the bore 12 between the middle section and the lower section 12m, 121. Accordingly, the bore 12 of the body is divided into three separate sections of gradually decreasing inner diameter. The upper section 12u of the bore communicates with the annulus through a number of ports 15 which extend radially through the wall of the body 11, allowing fluid communication between the upper section 12u of the bore and the outside of the body. The ports 15 are spaced circumferentially around the body 10.

The bore 12 receives a piston 20, which is slidable within the bore 12 between the two positions shown in Fig. 1 and Fig. 2. The piston 20 has an upper section 20u and a lower section 201. The outer diameter of the upper section 20u is greater than the outer diameter of the lower section 201. The outer diameter of the upper section 20u is a close tolerance fit with the inner diameter of the upper section 12u of the bore 12 through the body 11. Likewise, the outer diameter of the lower section 201 of the piston 20 is a close tolerance and a sliding fit with the inner diameter of the lower section 121 of the bore 12 through the body 11. A step in the outer diameter of the piston 20 is provided in the form of a downward facing shoulder 21u. The axial sliding of the piston 20 within the bore 12 of the body 11 is permitted by the sub 10, but the extent of axial sliding is limited by the interaction between the shoulders 21u and 13u.

The piston 20 has a second lower shoulder 211 also facing the bottom of the sub 10. The lower shoulder 211 is on the lower section 201 of the piston 20, and can therefore slide into the bore 12m of the middle section of the bore through the body 11. The downwardly facing shoulder 211 on the piston 20 and the upwardly facing shoulder 131 on the body 11 together restrain a spring 25, which is typically held in compression between the two shoulders 211 and 131. The compressive force of the spring reacts between the two shoulders to urge the piston 20 upwards relative to the body 11 of the sub 10.

The oppositely facing upper shoulders 21u, 13u of the piston and body typically each contain a respective magnetic element. In certain embodiments, these are provided by magnets disposed on each of the facing shoulders 21s and 13s, and the magnets are typically circumferentially aligned, so that they are pressed together on top of one another when the piston 20 is moved down the bore 12 and is in the open Fig. 2 configuration. However, it is sufficient for only one of the shoulders to bear a magnetic device which attracts the opposite shoulder, which can typically be a simple ferrous element without the inherent capacity to generate a separate magnetic field that is attracted by the magnet on the opposite shoulder. Magnets can optionally be provided on either shoulder, or both, and it is sufficient that a magnetic attractive force is established between the two shoulders. In the embodiment shown in Figs. 1 and 2, four magnets are provided on each of the shoulders 21u, 13u, and are circumferentially arranged around the shoulders, at approximately an equal spacing, although this is not essential, and in alignment with one another. Other arrangements of magnets with more or fewer magnets can be provided. The magnets on the respective shoulders are arranged so that they attract one another when the two magnets are within range of one another's magnetic field.

In the present embodiment, four magnets 24 are equi-distancedly spaced around the circumference of the downwardly facing shoulder 21u and are aligned with another four magnets 14 which are similarly spaced around the circumference of the upwardly facing shoulder 13u. In the present embodiment, the magnets 14 are optionally located on a mounting ring that is seated on the upwardly facing shoulder 13u. The magnets 24 and 14 are typically samarium cobalt magnets, but may also be neodymium magnets, or some other kind of magnet. The magnetic field generated by the magnets 24 and 14 is typically selected by choosing the strength and size of the magnet, and optionally adjusting its orientation within the sub 10, so that the magnets 24 are essentially out of range of the magnets 14 when the piston 20 is in the closed first position shown in Fig. 1.

As the piston 20 begins to move down the bore 12 within the body 11 the magnets 24 approach the magnets 14. Initially the magnets 14 and 24 are spaced far apart from one another so that the magnetic fields on each of them do not interact, and the magnetic attractive forces have little or no effect on the movement of the piston until the magnets 24, 14 come within range of one another. At that point the magnetic field of one magnet begins to attract the other magnet, thereby increasing the downward force applied to the piston 20 within the bore 12 as the magnets 24 approach the magnets 14.

The piston 20 is initially locked in a set rotational position by a spline on the body 11 which slides along an axial groove on the piston.

The piston is also sealed to the inner surface of the bore 12 at two locations. At the upper section of the piston 12u, a first upper seal 22u is provided at the large diameter section, and a second smaller diameter seal 221 is provided at the lower section 201 of the piston. The seals 22 are located on either side of the ports 15 when the piston 20 is in the first position, so the ports 15 are isolated from the bore 12 and fluid cannot pass through them from the bore. The difference in the sealed diameters between the upper and the lower seals 22 on the piston 20 cause the piston to move axially down the bore 12 of the body 11 in response to elevation of fluid pressure within the bore 12. Once the optional shear pin or other locking device has been deactivated and the piston 20 is free to move axially within the bore 12, an increase in the internal pressure of the fluid in the bore 12 creates the piston effect as a result of the differential piston area between the upper and the lower seals 22u, 221, and this force urges the piston axially downwards, counteracting the upward force of the compressed spring 25 between the shoulders 211 and 131. As the force applied by the differential piston areas continues to move the piston 20 down the bore 12, the magnets 24 gradually approach the magnets 14. The movement of the magnets closer together increases the magnetic force tending to attract the magnets towards one another, and causes an increase in the axial force tending to urge the piston 20 down towards the bottom of the sub 10. When the piston 20 has moved about half way between the two positions shown in Figs. 1 and 2, the magnetic attractive force that is tending to urge the downward movement of the piston 20 increases to the point where the combined force of the fluid pressure and the magnetic attraction acting in the downward direction overcomes the upwardly acting opposing spring force, and the piston 20 moves quickly down to the open position shown in Fig. 2. In the open position, the upper seals 20u on the piston 20 have moved underneath the ports 15 extending radially through the body 11, thereby uncovering them and allowing fluid communication from the bore 12 through the ports 15 and out into the annular area between the body 11 and the wellbore in which it is located.

Therefore, increasing the fluid pressure drives the piston down through the bore 12 until the magnets 24, 14 interact and the combined downward forces of the fluid pressure and the magnets overcome the upward force of the spring 25, thereby opening the ports 15 to allow circulation of fluid from the surface, through the bore 12 as shown in Fig. 2. This allows opening of the valve sub 10 to allow circulation of clean fluid at high pressure and flow rates at the level of the valve sub 10, which can be placed at any convenient location in the string. In fact, several valve subs 10 can optionally be placed at axially spaced locations in a string in order to provide axially spaced circulation ports. The different subs can be provided with different strengths of spring or magnet in order to trigger at different pressures, and can optionally be arranged in the string to trigger the lowest circulation sub first at the lowest pressure, followed by the second lowest etc., in order to wash the cuttings generated by the drill bit back through the annulus in an efficient manner without losing turbulence at the upper parts of the well.

Referring now to Figs 3 and 4, a second embodiment of a valve device in the form of circulation sub 110 has similar components to the circulation sub 10. Similar reference numerals will be used herein, but increased by 100. The sub 110 has a tubular body 111 with a central bore 112 extending axially through it. The second valve device 110 differs from the first 10 in the arrangement of the shoulders, spring and magnets. The bore 112 receives a piston 120, which is axially slidable within the bore 112, and has a wide upper section 120u and a narrower lower section 1201 with a downward facing shoulder 121 between them. At the lower end of the piston 120 there is provided a sleeve 104 which houses the magnets 124 associated with the piston 120. The sleeve 104 is generally in the form of a sleeve that has a bore that matches the inner diameter of the bore 112, and on its outer surface the sleeve 104 has a screw thread that engages with an internal thread on the inner surface of the end of the bore 112, whereby the sleeve screws onto the end of the piston 120. The magnet or magnets 124 are borne on the lower end of the sleeve 104 and face downwards.

The magnets 124 interact with magnets 114 associated with the body 111. The magnet or magnets 114 are in this embodiment provided on a sleeve 105 which screws into the lower end of the bore of the body 111 in a similar manner to the interaction between the sleeve 104 and the piston 120. The magnet or magnets 114 on the sleeve 105 are typically located on the upper end of the sleeve 105, facing upwardly, and in a suitable orientation to attract the magnets 124 when they come within range. Optionally the upper end of the sleeve 105 is received within the lower end of the sleeve 104 which can help to centralise the piston within the bore and reduce sticking due to misalignment during axial sliding. Optionally the sleeve 105 can accommodate the sleeve 104 within its bore instead. The spring 125 in the second embodiment is typically free floating between the lower shoulders 113 and an upper seal ring 126. The spring can be compressed as the piston 120 moves down the bore 112 in the same way as the previous embodiment. The compressive force of the spring 125 urges the piston 120 upwards relative to the body 111.

In the present embodiment, the downward axial sliding of the piston 120 within the bore 112 is limited by the interaction between the sleeve 104 and the sleeve 105.

As the piston 120 begins to move down the bore 112 the magnets 124 approach the magnets 114. Initially the magnetic attractive forces have little or no effect on the movement of the piston until the magnets 124, 114 come within range of one another. At that point the magnetic field of one magnet begins to attract the other magnet, thereby increasing the downward force applied to the piston 120 within the bore 112 as previously described.

The initial urge to move the piston 120 is provided by an increase in the internal pressure of the fluid in the bore 112 which urges the piston 120 axially downwards, counteracting the upward force of the compressed spring 125 and causing the magnets 124 gradually approach the magnets 114. The movement of the magnets closer together increases the magnetic force tending to attract the magnets towards one another, and causes an increase in the axial force tending to urge the piston 120 down towards the bottom of the sub 110. When the piston 120 has moved about half way between the two positions shown in Figs. 3 and 4, the magnetic attractive force that is tending to urge the downward movement of the piston 120 has increased to the point where the combined force of the fluid pressure and the magnetic attraction acting in the downward direction overcomes the upwardly acting opposing spring force, and the piston 120 moves quickly down to the open position shown in Fig. 4, with the sleeve 104 bottomed out on the sleeve 105.

In the open position, the ports 115 are uncovered and allowing fluid communication from the bore 112 through the ports 115 and out into the annular area between the body 111 and the wellbore in which it is located.

Thus, increasing the fluid pressure drives the piston down through the bore 112 until the magnets 124, 114 interact and the combined downward forces of the fluid pressure and the magnets overcome the upward force of the spring 125, thereby opening the ports 115 to allow circulation of fluid from the surface, through the bore 112 as shown in Fig. 2. This allows opening of the valve sub 110 to allow circulation of clean fluid at high pressure and flow rates at the level of the valve sub 110, which can be placed at any convenient location in the string.

Locating the magnets in sleeves spaced away from the spring means that the desig of the spring and the piston can be simpler. Referring now to Figs 5-7, a third embodiment of a valve in the form of circulation sub 210 has similar components to the circulation sub 10. Similar reference numerals will be used herein, but increased by 200.

The sub 210 has a tubular body 211 with a central bore 212 extending axially through it. The body 221 is formed in two subs: an upper sub and lower sub, defining three separate regions each with different respective diameters. The upper region 212 u with the narrowest diameter has a pin connection at the lower end of the upper sub which screws into a box connection on the upper end of the lower sub. The lower sub has a wide diameter region 212w at its upper end near the pin, which is wider than the bore of the upper sub. Below the central wider region 212w, the bore steps radially inwards forming an upwardly facing shoulder on the inner surface of the lower sub, above a lower region 2121. The inner diameter of the bore of the lower sub steps radially inwards again with a chamfer at the pin formed at the lower end of the lower sub. Thus the wide bore central region 212w of bore is wider than the narrower (lower) region 2121 of the lower sub. Therefore, the wide bore central region 212w at the top of the lower sub is disposed axially between a downward facing shoulder formed by the lower end of the pin of the upper sub, and an upward facing shoulder on the inner surface of the lower sub.

The third embodiment 210 differs from the first 10 in the orientation and direction of movement of the piston. The bore 212 receives a first piston 220, which is axially slidable within the bore 212. The first piston 220 has a wide head 220h and a relatively narrower upper section with an upward facing shoulder 220s between them.

At the upper end of the first piston 220 there is optionally provided a sleeve which houses the magnets associated with the first piston, but optionally, as they are in this embodiment, the magnets 224 associated with the piston are provided on an upper face of the first piston 220. The upper end of the first piston 220 typically has a finger sleeve 221 in the form of an arrangement of axially extending fingers spaced circumferentially around the bore, and connected to the piston 220 at their lower ends in a cantilever manner, so that they are able to move radially at their free upper ends, in relation to the bore, and in relation to one another. The upper end of each finger has a head 221h with a radially extending protrusion, biased radially outwards by the finger, and being adapted to be received in a shallow recess 212r on the inner surface of the bore. The recess 212r is located above the piston 220, and the protrusion on the head 221h of the finger sleeve 221 locks into the recess 212r , to resist axial movement of the finger sleeve 221, and thus the piston 220, within the bore 212. The gaps between the circumferentially spaced fingers extend axially along the length of the finger sleeve and allow the passage of fluid and the communication of fluid pressure radially through the finger sleeve 221, above the piston 220. At its lower end, the piston 220 has a second finger sleeve 222, with circumferentially spaced fingers allowing radial fluid communication like the first sleeve 221, but in the case of the second finger sleeve 222, the head 222h typically circumferentially connects the distal ends of the fingers rigidly together, and typically does not allow relative radial movement of the fingers. Instead, the head 222h provides a radially extending protrusion received within the bore of a second piston 230.

The second piston 230 has a head 230h at its upper end, which is sealed on its outer surface to the inner wall of the wide region 212w of the bore in the body of the lower sub. The outer diameter of the head 230h is larger than the inner diameter of the lower sub, and the downward travel of the second piston is limited by the upward facing shoulder on the inner surface of the lower sub. The annular upper face of the head 230h is flat. The second piston 230 has an inner bore, which narrows at the head 230h. The inner surface of the head 230h typically has a downwardly facing shoulder 230s on its inner surface, which is typically narrower than the head 222h of the first piston 220.

The head 222h of the finger sleeve 222 is disposed within the bore of the second piston 230, below the head 230h, so that the head 22h can slide axially into the bore of the second piston 230. Because the radial extension of the head 222h is larger than the throat at the head 230h of the second piston 230, and the head 222h has an upwardly facing shoulder 222s on its outer surface, which is disposed inside the bore of the second, lower, piston 230, the relatively large head 222h of the finger sleeve is retained within the bore of the second piston 230 by the downwardly facing shoulder 230s on the inner surface of the second piston 230. The shoulders 230s, 220s cooperate to allow the head 220h of the first piston to slide down into the bore of the second piston 230, without moving the second piston 230 as a result, and to allow limited upward movement of the head 220h on the first piston 220 within the bore of the second piston 230. Provided the shoulders 220s, 230s are not engaged, the second lower piston remains stationary during sliding movement of the head 220h in the bore of the second piston 230, but when the head 220h has moved up to the top of the bore of the second piston 230 and the shoulders 220s, 230s have engaged, further upward axial sliding of the first piston 220 pulls the head 230h and the rest of the lower second piston 230 along with it, to move axially up the bore.

The magnet or magnets 224 associated with the piston are typically borne on the upper end of the first piston 220 and face upwards. The magnets 224 interact with magnets 214 associated with the body 211. The magnet or magnets 214 are in this embodiment provided on the body 211, but could be provided on a sleeve in a similar manner to the embodiment of figs 3 and 4. The magnet or magnets 214 associated with the body 211 are typically located on a lower facing shoulder on the inner surface of the bore 212, and in a suitable circumferential position and orientation to attract the magnets 224 on the piston when they come within range. The main body of the first piston 220 is retained in the bore of the pin connection in the upper sub. The piston 220 is sealed by an outwardly facing seal disposed in a seal recess on the body of the piston above the head 220h, and compressed against the inner surface of the bore of the pin connection in the narrowest upper region 212u of the bore. The piston 220 cannot move down the bore to permit the seal to move out of the narrow bore 212u of the pin, because the head 221h of the first (upper) finger sleeve 221 is trapped in the recess 212r and resists downward movement of the piston 220. Below the seal on the body of the first piston, the seal on the outer surface of the head 220h is sealed to the inner surface of the wide bore central region 212w below the box of the lower sub. The sealed areas at each end of the piston 220 are therefore different, and the lower sealed area at the head 220h in the wide bore region 212w is larger than the upper sealed area on the body in the upper narrow region 212u. Therefore, increased fluid pressure within the bore of the piston 220 urges it upwards in the bore 212, as a result of the differential piston area.

The third embodiment has a first spring 225 which is typically held in compression between the head 220h of the first piston 220 and the lower end face of the pin connection. The spring 225 is compressed as the piston 220 moves up the bore 212 in the same way as the previous embodiment. The compressive force of the spring 225 urges the piston 220 downwards relative to the body 211, acting against the fluid pressure. When the fluid pressure in the bore 212 increases to a point at which the upward force on the piston (generated as a result of the differential piston areas) overcomes the downward force of the first spring 225, the first piston 220 begins to move up the bore 212 so that the magnets 224 associated with the piston approach the magnets 214 associated with the body. Initially the magnets are so far away from one another that magnetic attractive forces have little or no effect on the movement of the piston until the magnets 224, 214 come within range of one another. At that point the magnetic field of one of the (set of] magnets begins to attract the other, thereby increasing the upward force applied to the piston 220 within the bore 212.

The initial urge to move the piston 220 is thus typically provided by an increase in the internal pressure of the fluid in the bore 212 which urges the piston 220 axially upwards as a result of the differential piston area, counteracting the downward force of the compressed spring 225 and causing the magnets 224 to gradually approach the magnets 214. The movement of the magnets closer together increases the magnetic force tending to attract the magnets towards one another, and causes a gradual increase in the combined axial force tending to urge the piston 220 up the bore as the magnets close together. The strength of the magnets and the dimension of the clearance between them typically is set such that when the piston 220 has moved about half way between the two positions shown in Figs. 5 and 6, the magnetic attractive force that is tending to urge the upward movement of the piston 220 has increased to the point where the combined force of the fluid pressure and the magnetic attraction acting in the upward direction overcomes the downwardly acting opposing spring force, and the piston 220 moves quickly up to the open position shown in Fig. 6, with the piston 220 unable to move any further up the bore. Small equalisation ports 223 through the body prevent hydraulic locking of the first piston 220 as a result of axial movements.

In the open position, the lower piston 230 has been pulled up the bore as a result of the interaction of the heads 230h, 220h. The lower piston 230 has ports 230p disposed at its lower end, passing radially through the piston 230. The ports 230p are circumferentially aligned with ports 215 passing through the body. When the lower second piston 230 has been pulled up the bore and the magnets 214, 224 are touching, so that no further upward movement of the first piston 220 is possible, the ports 215 register with the ports 230p and allow fluid communication from the bore 212 through the ports 215 and out into the annular area between the body 211 and the wellbore in which it is located. The ports 215 are bounded by annular seals set in the inner surface of the lower region of the bore 2121 above and below the ports 215. Increasing the fluid pressure in the bore 212 drives the piston 220 up through the bore 212 until the magnets 224, 214 interact and the combined upward forces of the fluid pressure and the magnets overcome the downward force of the spring 225, thereby opening the ports 215 to allow circulation of fluid from the surface, through the bore 212. This allows opening of the valve 210 to allow circulation of clean fluid at high pressure and flow rates at the level of the valve sub 210, which can be placed at any convenient location in the string.

One optional feature provided in the third embodiment which is not shown in earlier embodiments resides in the upper finger sleeve 221. The fingers in the finger sleeve 221 are typically resiliently biased outwardly in a radial direction, and therefore are held in radial compression by the recess in the bore. The recess holding the radially compressed fingers is typically shallow, and while it resists free movement of the finger sleeve 221 in an axial direction, the resistance provided by the recess to hold the finger sleeve 221 in the same axial position is typically quite weak, and can be overcome by a relatively modest increase in fluid pressure tending to urge the piston 220 axially upwards in the bore as a result of the differential piston area. Therefore, the axial retention of the head of the finger sleeve 221 in the recess in the bore typically acts as a catch mechanism to resist premature axial movement of the finger sleeve (and therefore the piston 220) within the bore before the desired fluid pressure threshold has been reached. This effectively increases the activation threshold of the piston and delays the axial translation of the piston and subsequent uncovering of the circulation ports until the pressure threshold has been reached, thereby preventing the piston from prematurely triggering in the event of small transient kicks in the bore pressure, which are insufficient to generate the required force to dislodge the head of the finger sleeve from the recess. The pressure threshold required to overcome the resilient bias of the fingers, allowing them to escape from the recess and allow the piston to move axially in the bore, can be adjusted in different embodiments of the invention. Typically the required threshold is set so that small variations in wellbore pressure do not trigger the axial movement of the sleeve. Optionally, the relative sliding movement of the first and second pistons 220, 230 is controlled by a second spring 226 located between them, typically held in compression between the lower surface of the head 220h on the piston 220, and the flat upper surface of the head 230h on the second piston. Upward sliding of the second piston in an axial direction, relative to the first piston 220, compresses the second spring in between first and second pistons 220, 230. The compression of the second spring 226 typically urges the second piston down the bore into the position shown in Fig 6 in the absence of any other force acting on the second piston 230 to move it up the bore. Small equalisation ports 233 through the body prevent hydraulic locking of the second piston 230 as a result of axial movements. Typically, the second spring is typically always held in compression.

Fig 7 shows the third embodiment 210 set in reverse circulation mode, where the fluid pressure in the bore 212 is relatively low, and is insufficient to free the head 221h from the recess 212r and trigger the axial upward movement of the first piston 220 into the open position. Fluid is being pumped from the surface down through the annulus with the intention to flow the fluid in through the ports 215 at the lower end of the device into the bore 212 without triggering the axial movement of the first piston. In order to achieve this, the annular pressure is gradually increased to a threshold below the triggering threshold required to move the first piston 220.

Initially, the device is in the position shown in Fig 5, with the port 215 closed as the second piston 230 is forced axially downward by the expansion of the second spring 226. However, as the annular pressure increases, the small ports 233 connecting the annulus to the sealed chamber beneath the head 230h of the second piston 230 allows communication of fluid pressure from the annulus outside the tool into the annular chamber between the second piston 230 and the body 210. The force applied by the spring 226 to the second piston 230 to urge it axially down the bore 212 is relatively weak, because the spring 226 is typically relatively weaker than the spring 225. Therefore, a low threshold of fluid pressure is eventually reached in the annular chamber underneath the sealed head 230h of the second piston 230, and this causes the second piston 230 to travel axially upwards in the bore 212, compressing the second spring 226.

The upward axial force applied by the compression of the second spring 226 is insufficient to trigger axial movement of the first piston 220, because the first spring 225 is much stronger than the second spring 226. Therefore, the first piston 220 remains in the same position, while the second piston 230 moves axially up the bore relative to the first piston 220, eventually reaching the position shown in Fig 7.

In the Fig 7 configuration, the ports 230p have moved into axial alignment with the ports 215 passing through the body, and this allows fluid to flow from the annulus outside the tool into the bore 212, and back to the surface by passing axially upwards through the bore 212 and the string above it. Typically, the bore 212 is closed below the tool in reverse circulation operations. The annular pressure also acts on the first piston 220 through the small ports 223, pressing it downwards in the bore 212, and preventing it from activating. When the reverse circulation operation has been completed, the annular fluid pressure is reduced from surface, and eventually the force of the second lower spring 226 overcomes the reducing fluid pressure acting on the second piston 230, returning it to the position shown in Fig 5, where the ports 215 are occluded by the lower piston 230 and the bore 212 is closed.

Embodiments of the invention have the advantage that the valve sub can be triggered at comparatively low fluid pressures, which allows more valve subs to be placed within the string and arranged to be triggered at different pressure ranges, all within the acceptable operating ranges of the existing pump already provided at the surface. Modifications and improvements can be incorporated without departing from the scope of the invention.

Claims

1 A valve control device having a bore with a piston member axially moveable in the bore between first and second configurations, wherein the piston is urged to move axially between the first and the second configurations within the bore by fluid pressure applied to the piston, and wherein the axial movement of the piston from the first to the second configuration under the force of the fluid pressure is opposed by the force of a spring device, wherein the piston is urged by a magnetic force to move axially from the first to the second configuration in the same direction as the force applied by the fluid pressure, and against the force of the spring device, and wherein the magnetic force applied to the piston when the piston is in the first configuration is less than the magnetic force applied to the piston when the piston is in the second configuration, whereby as the piston approaches the second configuration under the force of the fluid pressure, the magnetic force increases as the piston moves under the force of the fluid pressure, whereby the magnetic force and the fluid pressure together overcome the force of the spring device to move the piston into the second configuration.

2 A device according to claim 1, wherein the force applied to the piston by the spring device is greater than the magnetic force applied to the piston when the piston is in the second configuration.

3 A device according to claim 1 or claim 2, wherein the valve is closed when the piston is in the first configuration, whereby fluid flowing through the bore of the valve is not diverted from the bore.

4 A device according to any preceding claim, wherein the valve is open when the piston is in the second configuration, whereby fluid flowing through the bore of the valve is diverted from the bore to another location outwith the bore of the valve. 5 A device according to any preceding claim, wherein the magnetic forces are applied by at least two magnets, one of which is associated with the piston and is moveable in relation to the bore, and the other of which is disposed in a fixed location relative to the bore.

6 A device according to claim 5, wherein more than two magnets are provided.

7 A device according to claim 5 or claim 6, wherein magnets are arranged in pairs, with one of each pair associated with the piston, and the other disposed in the fixed location relative to the bore, and wherein the magnets in each pair are oriented relative to one another in the valve device so that the magnetic field generated by each magnet of each respective pair is arranged to attract the other magnet of the pair when the piston moves axially to move the magnets within range of one another.

8 A device according to claim 7, wherein the pairs of magnets are circumferentially aligned, so that they are moved axially together when the piston moves in the bore into the second configuration. 9 A according to any one of claims 7 and 8, wherein more than one pair of magnets is provided.

10 A device according to any preceding claim, wherein at least one magnet is mounted on the piston.

11 A device according to any one of claims 5-9, wherein the or each magnet associated with the piston and being movable relative to the bore is carried on a member that moves with the piston. 12 A device according to any preceding claim, wherein the piston is a tubular piston, and the bore of the valve device passes through the piston. 13 A device according to any preceding claim, wherein the piston comprises a sliding sleeve, which slides within a body through which the bore extends. 14 A device according to any preceding claim, wherein the valve device has a body, wherein the valve device incorporates an anti-rotation device by which the piston is keyed to the body to avoid rotation relative to the body.

15 A device according to any preceding claim, wherein the piston is adapted to be locked in the first configuration by locking device that retards the movement of the piston.

16 A device according to claim 15, wherein the locking device is adapted to be opened to allow the piston to move relative to the bore by fluid pressure rising above an unlocking threshold.

17 A device according to any preceding claim, wherein the piston is sealed to the inner surface of the bore by first and second seals at two axially spaced locations along the piston, and wherein the first and second seals define different surface areas, which cause the piston to move axially within the bore in response to the application of fluid pressure to the piston.

18 A device according to any preceding claim, wherein the piston comprises a ball catcher with a throat adapted to catch a ball or other activation device dropped into the bore from the surface, whereby in the event of failure of the locking device, the device can be operated to move the piston into the second configuration by dropping a ball or other activation device into the ball catcher and retaining it in the throat. 19 A device as claimed in any preceding claim, comprising a catch mechanism adapted to arrest the movement of the piston below a fluid pressure threshold necessary for releasing the catch device and allowing movement of the piston. 20 A valve having a device as claimed in any preceding claim.

21 A string for use in a wellbore, comprising at least first and second valve control devices according to any one of claims 1-19, placed at axially spaced locations in the string, wherein the first device is configured to move the piston from the first to the second configuration at a first fluid pressure, and wherein the second device is configured to move the piston from the first to the second configuration at a second fluid pressure, and wherein the second fluid pressure is different from the first fluid pressure. 22 A method of actuating a valve, the valve comprising a bore with a piston member axially moveable in the bore between first and second configurations, and wherein the axial movement of the piston from the first to the second configuration is opposed by the force of an energised spring device, wherein the method includes the steps of:

- applying fluid pressure to the piston and urging the piston to move axially between the first and the second configurations within the bore to compress and energise the spring device as a result of the fluid pressure applied to the piston; and

- generating a magnetic force acting on the piston to move the piston axially from the first to the second configuration in the same direction as the force applied by the fluid pressure, and against the force of the spring device;

- wherein the magnetic force applied to the piston when the piston is in the first configuration is less than the magnetic force applied to the piston when the piston is in the second configuration, whereby as the piston approaches the second configuration under the force of the fluid pressure, the magnetic force increases as the piston moves under the force of the fluid pressure, whereby the magnetic force and the fluid pressure together overcome the force of the spring device to move the piston into the second configuration.

23 A method according to claim 22, wherein the spring device has a strong spring force which is higher than the fluid pressure force, but lower than the combined fluid pressure force and magnetic force when the piston is approaching the second configuration.

24 A method according to claim 22 or claim 23 wherein the spring force is larger than the magnetic force when the piston is in the first configuration.