Hydraulic circuit and method for operating a sealing device

A hydraulic circuit and method for operating a hydraulic device according to which fluid is passed from a source to the device while some of the fluid is passed to a valve that is adjustable to control the amount of fluid passed to it and therefore the amount of fluid passed to the device.

BACKGROUND

The present invention relates generally to operating a hydraulic device and in particular to a hydraulic circuit connected to a stripper for sealing off and holding wellbore fluids in a well, and a method of controlling the sealing of tubing associated therewith.

Coiled tubing injectors are used to grip and advance coiled tubing into a well via a wellhead. Many coiled tubing injectors utilize a stripper to seal off and hold wellbore fluids in the well. The stripper, also called a stripper/packer, lubricator, or stuffing box, is typically positioned above the wellhead and utilizes one or more hydraulic actuated cylinders to press stripper elements (or pack-off elements) against the coiled tubing while the tubing is being inserted into or removed from the well, thereby sealing the wellhead and preventing the release of wellbore fluids from the well. The cylinder or cylinders in the stripper are controlled using a stripper hydraulic circuit connected thereto.

Several potential problems arise during the operation of a typical stripper hydraulic circuit. For example, if the diameter of the tubing increases during the operation of a typical stripper hydraulic circuit, there may be an unsafe pressure increase in the circuit. Also, many stripper hydraulic circuits require a human operator to move near the stripper during operation to adjust the sealing pressure on the tubing, thus increasing the risk of harm to the operator. Further, if there is a loss of pressure to the stripper hydraulic circuit, the seal against the tubing will be broken and wellbore fluids will be released from the wellhead, creating both a safety and environmental hazard and possibly damaging any equipment in the vicinity of the wellhead.

Current solutions to a loss of pressure in the stripper hydraulic circuit include using a shut-off valve to isolate the stripper hydraulic circuit after the loss of pressure, or connecting a check valve upstream of the stripper hydraulic circuit to hold pressure in the stripper hydraulic circuit. Although these solutions prevent a complete loss of pressure to the stripper hydraulic circuit, they do not provide an easy way for the human operator to resume control of the stripper hydraulic circuit after the pressure has been restored. In addition, neither of these solutions enables the sealing pressure on the tubing to be increased in the event of a loss in pressure to the hydraulic circuit or other unforeseen emergency.

Therefore, what is needed is a hydraulic circuit for controlling a stripper that overcomes these problems.

DETAILED DESCRIPTION

Referring toFIG. 1, the reference numeral10refers to a coiled tubing injector positioned above a well12. A wellhead14extends above the well12, and a stripper16extends above the wellhead14.

A spool of coiled tubing18is positioned at a predetermined location away from the injector10. Unspooled tubing20passes from the spool18and under a measuring device, such as a wheel22, and between several (seven in the example ofFIG. 1) pairs of opposed rollers24rotatably mounted to an arcuate support platform26. The tubing20then passes from the last pair of rollers24into the injector10. The injector10includes a frame28inside of which a pair of carriages are mounted (not shown). The carriages of the injector10drive the tubing20into the stripper16for passage through the wellhead14and into the well12.

Referring toFIG. 2, a hydraulic actuated cylinder30is connected to the stripper16(not shown) in a conventional manner and includes a piston30athat reciprocates in a cylinder housing in response to hydraulic fluid being introduced into, and discharged from, the cylinder housing, in a conventional manner. One end of a rod30bis connected to the piston30aand a portion of the rod30bextends out from the cylinder30, and is engaged with the stripper16in a conventional manner.

The cylinder30is connected in a hydraulic circuit, generally referred to by the reference numeral32, so that fluid is selectively introduced and discharged from the cylinder30to cause corresponding extension and retraction of the cylinder30, as will be further described. This extension and retraction of the cylinder30causes the stripper16to sealingly engage the tubing20, and to release the tubing20, respectively, in any conventional manner. For example, two arcuate or semi-circular elements may extend around the tubing20, and the rod30bmay be connected to one element so that extension of the cylinder30causes the one element to move towards the other and press against the tubing20, thereby sealingly engaging the tubing20.

The circuit32includes a source34of pressurized hydraulic fluid which is connected to a pressure reducing valve36in the circuit via a line38. An output from the pressure reducing valve36is connected to a switching valve40via a line42. An output from the switching valve40is connected to a check valve44via a line46that also extends from the check valve44to the input of a control valve48. The check valve44permits fluid flow in a direction indicated by the flow arrows, but prevents flow in the opposite direction. An accumulator50is connected to the line46between the check valve44and the control valve48via a line52. The accumulator50is adapted to store fluid from the circuit32and introduce the stored fluid into the circuit32under conditions to be described.

An output from the control valve48is connected to a counterbalance valve54via a line56. The counterbalance valve54is normally closed but can be opened under conditions to be described. A line58extends from the line56at a location downstream of the control valve48to a check valve60and, from the check valve60, to the line46at a location upstream of the control valve48. The check valve60permits fluid flow in a direction indicated by the flow arrows, but prevents flow in the opposite direction. It is understood that the control valve48includes a relief mechanism (not shown) and its function will be described in detail.

The counterbalance valve54is also connected to a line62which, in turn, is connected to one end portion of the cylinder30. Thus, fluid flows from the source34, through the valves36,40,44,48and54and to the cylinder30for actuating the cylinder30in a manner to be described. It is understood that the counterbalance valve54includes a check valve that will permit fluid flow in this manner but will prevent fluid flow in the opposite direction.

Another output from the control valve48is connected to a counterbalance valve64via a line66that extends to a relief valve68. The counterbalance valve64is normally closed but is opened under conditions to be described, and the relief valve68is adjustable to control pressure reduction across the control valve48, from the line46to the line56. The control valve48is configured to allow some fluid to pass through it from the line46to the line56, while allowing some fluid to be diverted, or bled off, from the control valve48to the line66and the counterbalance valve64, for passage to the relief valve68, all under conditions to be described.

The source34is also connected to a switching valve70via a line72. The switching valve70is connected to the counterbalance valve54via a line74, and is connected to the counterbalance valve64via the line74and a line76. The lines74and76act as pilot lines for the counterbalance valves54and64, respectively, and, as such, control the operation of the valves.

The relief valve68and the switching valve70are connected to an exhaust tank78via lines80and82, and the line82, respectively. The switching valve70normally connects the line74to the source34via the line72, but is adapted to be switched to terminate this connection and connect the line74to the tank78via the line82, under conditions to be described.

The pressure reducing valve36is connected to the tank78via a line84and the line82, and is configured to allow some fluid to pass through it from the line38to the line42, while allowing some fluid to be diverted from the pressure reducing valve36to the tank78, all under conditions to be described.

The switching valve40is connected to the tank78via a line86and the line82, and is also connected to the other end portion of the cylinder30via a line88to enable fluid to flow from the cylinder30to the tank78via the switching valve40and the lines88,86and82, as indicated by the flow arrows. The switching valve40normally connects the line42to the line46, and the line88to the line86. However, the switching valve40is adapted to be switched so that it connects the line42to the line88, and connects the line46to the line86, under conditions to be described.

The line88is also connected to a pilot-operated check valve90, via a pilot line92, and the check valve90is, in turn, connected to the line58via a line94that extends from the line58to the line82. The check valve90normally prevents flow through the line94and is adapted to open when fluid is received from the pilot line92to permit flow through the line94and to the tank78via the line82, as indicated by the flow arrows and under conditions to be described.

The control valve48is connected to the tank78via a line96and the line82. Thus, fluid can be discharged from the control valve48into the tank78under conditions to be described.

The counterbalance valves54and64are normally closed, but are adapted to open in response to a predetermined fluid pressure being applied to the valves by the lines74and76, respectively. When the counterbalance valve54is in its open position, fluid is allowed to flow from upstream of the control valve48, through the valves48and54, and to the cylinder30as indicated by the flow arrows. Fluid is allowed to flow in the reverse direction from the cylinder30, through the counterbalance valve54and to the tank78, either via the control valve48or via the check valves60and90in a manner to be described. When the counterbalance valve54is in its closed position, fluid is still allowed to flow from upstream of the control valve48to the cylinder30via the valve48and the check valve included in the counterbalance valve54. However, reverse fluid flow from the cylinder30to the tank78via the counterbalance valve54is not allowed when the counterbalance valve54is in its closed position.

When the counterbalance valve64is in its open position, fluid is allowed to flow from the control valve48to the relief valve68as indicated by the flow arrows. When the counterbalance valve64is in its closed position, fluid is not allowed to flow from the control valve48to the relief valve68. Reverse fluid flow through the counterbalance valve64, that is, fluid flow from the relief valve68to the control valve48, is not possible, regardless of whether the counterbalance valve64is in its open or closed position.

Assuming that the tubing20(FIG. 1) is passed into the injector10in the manner described above and it is desired to extend the cylinder30so that the stripper16sealingly engages the tubing20for the purpose of preventing the release of wellbore fluids from the well12, an appropriate valve, pump or the like (not shown), associated with the source34is activated. Thus, pressurized fluid flows into the line38and pressurizes the line38up to the pressure reducing valve36. The pressure reducing valve36is set to pass a portion of this fluid to the switching valve40in the manner discussed above, reducing the pressure across the valve36, that is, from the line38to the line42to a pressure corresponding to the maximum sealing pressure that the stripper16may exert on the tubing20.

Assuming the switching valve40is in its normal mode in which it connects the line42to the line46, the lines42and46are pressurized. Thus, pressurized fluid flows into the line46and pressurizes that portion of the line46extending to the control valve48to the above pressure corresponding to the maximum sealing pressure that the stripper16may exert on the tubing20. The control valve48is set to pass a portion of this fluid to the cylinder30in the manner discussed above, which portion is sufficient to establish a normal operating fluid pressure in the cylinder30that corresponds to the normal operating sealing pressure that is exerted by the stripper16on the tubing20. The remaining portion of the fluid from the control valve48will bleed off and pass through the line66, the counterbalance valve64, and to the relief valve68.

Pressurized fluid also flows from the source34to the switching valve70. Assuming that the valve70is in its normal mode in which it connects the source34to the line74, fluid flows from the source34, through the line72and the switching valve70, and to the lines74and76to pressurize the lines74and76. The counterbalance valves54and64are normally closed and the lines74and76, respectively, serve as pilot lines for the valves54and64and thus open the valves54and64and allow pressure to be transmitted through the valves54and64.

The output pressure from the control valve48is transmitted to one end of the cylinder30via the line56, the counterbalance valve54and the line62. Assuming that the rod30bof the cylinder30is in a retracted position as a result of a previous operation, the rod30bwill extend when subjected to this pressure, thus causing the stripper16to apply a sufficient amount of load against the tubing20to sealingly engage the tubing. Assuming the switching valve40is in its normal mode in which it connects the line88to the line86, the extension of the cylinder30will force fluid from the other end of the cylinder30to the switching valve40via the line88, and to the tank78via the lines86and82, as shown by the flow arrows.

Due to the opening of the counterbalance valve64, some of the fluid from the control valve48will bleed off and pass through the line66, the counterbalance valve64, and to the relief valve68. The control valve48and the relief valve68are designed so that the relief valve68can control the amount of fluid that can be bled off from the control valve48in the above manner, and therefore the fluid pressure passing to the cylinder30. In particular, to increase the amount of sealing pressure on the tubing20, the relief valve68is adjusted to reduce the amount of flow being bled off from the control valve48, thereby increasing the output pressure in the line56and the amount of pressure applied to the cylinder30and the sealing pressure on the tubing20. To decrease the amount of sealing pressure on the tubing20, the relief valve is adjusted to increase the amount of flow being bled off from the control valve48, thereby decreasing the output pressure in the line56.

When the fluid applied to the cylinder30is at the desired pressure corresponding to the desired sealing pressure, or load, that the stripper16exerts on the tubing20, the relief valve68is no longer adjusted and the output pressure in the line56remains constant, thereby applying constant loading on the tubing20.

In situations where the tubing20is part of a string having a varying diameter, constant pressure on the cylinder30can always be maintained despite the fact that the diameter of the tubing20varies as it passes through the stripper16. Specifically, if the diameter of the tubing20increases during the above mode, it causes a corresponding retraction of the cylinder30from the above-described extended position. However, an unsafe pressure increase in the cylinder30is avoided because the fluid in the cylinder30will be forced out of the cylinder30and will flow to the control valve48through the line62, the counterbalance valve54and the line56in a direction opposite that shown by the arrows inFIG. 2. This reverse fluid flow through the counterbalance valve54is possible because the counterbalance valve54is still open due to the fluid pressure being applied to the counterbalance valve54by the line74. This reverse fluid flow triggers the above-mentioned relief mechanism in the control valve48in a conventional manner, enabling fluid to flow from the control valve48to the tank78via the lines96and82. Thus, only as much fluid as necessary flows from the cylinder30to the tank78in order to maintain constant pressure on the tubing20. If the diameter of the tubing20decreases, additional fluid will enter the cylinder30from the source34via the control valve48in the manner described above, thereby maintaining constant pressure on the cylinder30and thus the tubing20. Also, if additional fluid is unavailable from the source34, additional fluid may enter the cylinder30from the accumulator50via the control valve48and the counterbalance valve54.

Assuming that the stripper16is exerting sealing pressure on the tubing20in accordance with the foregoing, if there is a significant loss in the fluid pressure available from the source34for whatever reason, the pressure level in the line46, which is normally at the maximum sealing pressure discussed above, will drop significantly. When this occurs, there is no immediate effect on the pressure in that portion of the line46downstream of the check valve44or the accumulator50because the check valve44maintains the maximum sealing pressure downstream from its location in the line46. Likewise, the closed check valve90prevents fluid from flowing from the line46to the tank78via the lines94and82, thereby holding the pressure level in the line46downstream of the check valve44at the maximum sealing pressure.

In response to any significant loss in the fluid pressure available from the source34, the pressure in the lines72and74also drop accordingly. Since the line74serves as the pilot line for the counterbalance valve54, this pressure drop causes the counterbalance valve54to close, thereby holding the sealing pressure in the cylinder30. Similarly, the pressure drop in the line74causes a pressure drop in the line76, thus causing the counterbalance valve64to close and prevent fluid from being bled off from the control valve48via the line66.

Also in response to the above significant loss in the fluid pressure available from the source34, the normal operating pressure placed on the cylinder30will not only be maintained as discussed above, but the pressure on the cylinder30will be increased for safety purposes. In particular, the output pressure of the control valve48, and therefore the pressure on the cylinder30, will increase because initially the pressure in the line46downstream of the check valve44is higher than the pressure in the line56and fluid can no longer be bled off from the control valve48via the line66, as discussed above. This pressure increase is possible due to the fact that the above-mentioned check valve included in the counterbalance valve54will allow pressure to be transmitted to the cylinder30, but will prevent pressure to be transmitted in the opposite direction from the cylinder30, even though the counterbalance valve54is closed. Also, additional fluid provided to the line46by the accumulator50will be transmitted to the cylinder30through the control valve48, the check valve included in the counterbalance valve54, and the lines56and62, to place additional pressure on the cylinder30. Thus, the cessation of pressure bleeding from the control valve48and the additional pressure provided by the accumulator50will result in the sealing pressure provided by the cylinder30rising to a value that is significantly higher than the normal operating sealing pressure.

When the full fluid pressure in the source34is restored, the counterbalance valves54and64will automatically open again, allowing pressure to be bled off from the control valve48, thereby reducing the pressure on the cylinder30. The sealing pressure will then be able to be controlled as usual by the relief valve68. Thus, the operator does not have move near the stripper16to restart normal stripper16control and operation.

The circuit32is also adapted to operate in an emergency mode in the event it is desired to terminate normal operation of the stripper16for some unforeseen reason. In this case the operator would manually switch the switching valve70so that the above-mentioned connection between the line74and the source34is terminated and a connection is established between the line74and the tank78via the line82, as discussed above. Thus, fluid in the line74is passed to the tank78resulting in a significant pressure drop in the line74, similar to the pressure drop experienced when the fluid pressure at the source34is lost as discussed above.

When the pressure in the line74drops, the counterbalance valve54closes, thus holding the sealing pressure in the cylinder30. Similarly, the counterbalance64closes due to the drop in pressure in the line74and therefore the line76, thus preventing pressure from being bled off from the control valve48. As a result, the pressure at the control valve48, and therefore the pressure in the line56, increases and is transmitted to the cylinder30via the check valve included in the closed counterbalance valve54, as discussed above, and the line62. The output pressure will increase all the way up to the maximum sealing pressure since the source34is still pressurized and the pressure reducing valve36still operates to reduce the source34pressure in the line38to the maximum sealing pressure in the line42. Thus, the accumulator50does not have to provide additional pressure to the cylinder30as in the previous mode. The output pressure of the control valve48, and therefore the pressure placed on the cylinder30, ceases to increase and remains constant after reaching the maximum sealing pressure.

The cylinder30will remain at the maximum sealing pressure until the operator manually switches the switching valve70to connect the line74back to the source34upon resolution of the emergency situation. When this occurs, the pressure in the line74will increase back up to the source34pressure, resulting in the opening of the counterbalance valves54and64. This allows the resumption of pressure bleeding from the control valve48, thereby decreasing the pressure placed on the cylinder30via the open counterbalance valve54. The operator may then control the sealing pressure using the relief valve68, as described above.

When it is desired to unseal the tubing20, the cylinder30is moved from its extended position discussed above to its retracted position. To achieve this opening action, the switching valve40is switched to connect the line42to the line88, and to connect the line46to the line86. This results in fluid flowing to the cylinder30via the pressure reducing valve36, the switching valve40, and the lines38,42and88. The fluid flows in the lines38and42in the direction of the corresponding flow arrows shown inFIG. 2. However, the fluid flows in the line88in a direction opposite the direction of the corresponding flow arrows. As a result, the cylinder30retracts, forcing fluid out of the cylinder30, through the line62, the counterbalance valve54, the line56, the line58, the check valve60, and to the line94, also in a direction opposite the flow arrows (with the exception of the flow arrow for the line58).

Fluid is allowed to flow through the counterbalance valve54since the line74is still pressurized at the source34pressure, which maintains the counterbalance valve54in its open position. Also, although fluid will not flow from the line56to the line46through the control valve48, fluid will flow from the line56into the line58and to the check valve60. Since the pressure in the line56is greater than the pressure in the line46, the check valve60will open causing the fluid to flow, via the line58to the line94. Pressurization of the line88also results in the pressurization of the pilot line92, which opens the check valve90to allow fluid to flow from the line58, through the lines94and82, and to the tank78. As a result, the fluid discharging from the cylinder30is allowed to drain to the tank78. Also, the opening of the check valve90allows the fluid stored in the accumulator50to discharge to the tank78via the lines52,46,58,94and82.

During this cylinder30open mode, the counterbalance valve64remains open because the lines74and76are still pressurized at the source34pressure as discussed above. However, pressure is not bled off from the control valve48to the counterbalance valve64since the pressure in the line56is greater than the pressure in the line46and therefore the counterbalance valve64is not employed.

VARIATIONS

It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, although one cylinder30is used in the stripper16and the circuit32, the quantity of cylinders30may be increased.

Moreover, other types of valves may be substituted for the valves employed in the exemplary embodiment. For example, a pilot-operated check valve may be substituted for each counterbalance valve employed in the exemplary embodiment. Also, in addition to the injector10and the stripper16, other configurations and/or types of injectors and strippers may be employed in conjunction with the circuit32.

Further, pressure gauges may be connected to the circuit32at various locations. For example, a pressure gauge may be connected to the line62to measure the pressure in the cylinder30. Also, an adjustable needle valve may be connected to the line38and may be closed after normal operation of the circuit32has begun, thereby preventing any fluid flow from the source34to the pressure reducing valve36.

Still further, one or more of the circuits32may be employed in conjunction with the stripper16or with other types of strippers that include hydraulic actuated cylinders, and each circuit32may be independently controlled. These circuits32may all be connected to the same source34, or the circuits32may be connected to separate and independent sources34.

Still further, the circuit32may be modified so that it is comprised of two or more sub-circuits, with each sub-circuit essentially equivalent to the circuit32as shown in the exemplary embodiment. Such a modification may be carried out for redundancy purposes. For example, if the circuit32is comprised of two symmetric sub-circuits and if during operation one of the sub-circuits breaks and leaks fluid, the pressure in the cylinder30or cylinders30associated with the broken sub-circuit will drop significantly. However, the pressure in the cylinder30or cylinders30of the operational sub-circuit will still be able to maintain 50% of the stripper sealing pressure. In such an example, it is understood that one switching valve40, one relief valve68, one switching valve70, and/or one source34, or any combination thereof, may be employed to connect to and serve both sub-circuits.

It is understood that any foregoing spatial references, such as “side,” “above,” etc., are for the purpose of illustration only and do not limit the specific spatial orientation of the structure described above. It is also understood that the above-described circuit32is not limited to the application of pressure sealing as discussed above, but can be easily adapted to other applications.

Although an exemplary embodiment of this invention has been described in detail above, those skilled in the art will readily appreciate that many other variations and modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of this invention. Accordingly, all such variations and modifications are intended to be included within the scope of this invention as defined in the following claims.