Abstract:
The present invention has been contemplated to meet the above described needs. In a broad aspect, the invention may include a subsurface safety valve for controlling a fluid flow through a well conduit comprising a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing, a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position, a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions, a primary piston member in operative communication with the flow tube and a secondary piston member in operative communication with the flow tube.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to subsurface well equipment and, more particularly, to a subsurface safety valve.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     The use of subsurface safety valves in oil and gas wells is well known. U.S. Pat. No. 4,660,646 to Blizzard, which is fully incorporated herein by reference, describes the use of a “flapper” type valve disposed within the well bore which is opened and closed with a flow tube, generally a cylindrical tube which moves telescopically within the well bore. The Blizzard flow tube is actuated using a piston and cylinder assembly. One of the piston or cylinder is attached to the flow tube, and when hydraulic pressure is applied to the piston, the piston moves down as does the flow tube, thereby actuating the safety valve to an open position.  
         [0003]     It is also well known that the fluid column acting on the piston and cylinder assembly to open the subsurface safety valve applies ever greater pressure the deeper the piston and cylinder assembly is set into the earth. Therefore, the force required to lift the flow tube, and close the valve, increases accordingly. Generally, spring force and sometimes hydraulic pressure is used to lift the flow tube and close the valve. Occasionally, the piston and cylinder assembly used to lift the flow tube fails due to seal wear or other well known mechanical failure. In the case of such a mechanical failure, if the aforementioned spring is not strong enough to overcome the force applied by the fluid column, the valve will fail in the open position. A failure in the open position is generally undesirable as being unsafe, and operationally inefficient. As such, various techniques have been employed to ensure that in the event of a failure, the valve will fail in the closed position.  
         [0004]     The present invention is directed to a subsurface safety valve that, in the event of a failure, fails in the closed position.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention has been contemplated to meet the above described needs. In a broad aspect, the invention may include a subsurface safety valve for controlling a fluid flow through a well conduit comprising a housing having a bore and disposed within an annulus defined by the space between the well conduit and the housing, a valve closure member movable between an open position and a closed position, and adapted to restrict the fluid flow through the bore when in the closed position, a flow tube moveably disposed within the housing and adapted to shift the valve closure member between its open and closed positions, a primary piston member in operative communication with the flow tube and a secondary piston member in operative communication with the flow tube. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]     For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings wherein:  
         [0007]      FIG. 1  is a schematic view in section and elevation of a typical well completion including a subsurface safety valve.  
         [0008]      FIG. 2A  is a fragmentary elevational view, partly in cross section, showing a typical flapper type safety valve in an open position.  
         [0009]      FIG. 2B  is a fragmentary elevational view, partly in cross section, showing a typical flapper type safety valve in a closed position.  
         [0010]      FIG. 3A  shows a schematic view of a primary hydraulic system for a safety valve constructed in accordance with the present invention.  
         [0011]      FIG. 3B  shows a schematic view of a secondary hydraulic system for a safety valve constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]     For purposes of this description, the terms “upper,” “lower,” “up,” “down,” “uphole,” and “downhole” are relative terms to indicate position and direction of movement in easily recognized terms. Usually these terms are relative to a line drawn perpendicularly downward from the center of the borehole at the earth&#39;s surface, and would be appropriate for use in straight, relatively vertical wellbores. However, when the wellbore is highly deviated, such as from about horizontal to about 60 degrees from vertical, or if there are multiple laterals, these usually comfortable terms to persons skilled in the art may not make sense. Use of these terms are for ease of understanding as an indication to what relative position or movement would be if the well were vertical, and should not be construed to limit the scope of the invention.  
         [0013]     Referring to  FIG. 1 , an exemplary environment within which the present invention may be used is shown as a conventional oil and gas production well or well completion  10 , as is known in the art. The illustrated well completion  10  includes a casing string  12  extending from the well surface  13  to a hydrocarbon production formation (not shown). A tubing string  14  is shown concentrically disposed within the casing string  12 , and extends from a wellhead  16  through a production packer  18 . The production packer  18  of  FIG. 1  seals the annulus formed between the tubing and casing strings  14 ,  12 , and directs formation fluids, such as oil, gas and water, into the tubing string  14  that are admitted into the well bore  19  through perforations (not shown) in the casing string  12 . Valves  20 ,  22 , which are helpful in controlling fluid flow from the tubing string  14 , are shown at the well surface  13 . A wellhead cap  24  is useful, for example, to permit servicing the well  10  via tubing string  14  with wireline equipment (not shown).  
         [0014]     Still referring to the exemplary environment of  FIG. 1 , a flow control device  30  is shown installed in the well  10  as a part of the tubing string  14  to assist in controlling fluid flow to the well surface  13  through the tubing string  14  from downhole, as is also known in the art. The illustrated flow control device  30  is a conventional, surface-controlled subsurface safety valve  32  connected in the tubing string  14 , such as by suitable threaded connections. The device  30  may be operated, for example, by control fluid conducted from a hydraulic manifold  40  at the well surface through a control line conduit  42 . Further explanation of the components, arrangement and operation of a conventional well completion and related equipment can be found in prior art patents and other publications, such as U.S. Pat. Nos. 4,723,606, 4,624,315 and 5,127,476, each of which is hereby incorporated by reference herein in its entirety.  
         [0015]     The above description and further aspects of a conventional well completion having one or more underground oilfield tubulars and a subsurface safety valve are known in the art and in no way limiting upon the present invention or the appended claims. Moreover, the present invention is not limited to use in the environment of a well completion, oil and gas production well or oilfield tubular, but may be used in any environment where it is desired to be able to retain a valve member of a flow control device having a bore in an open position.  
         [0016]     Now referring to  FIGS. 2A and 2B , the illustrated safety valve  32  is a conventional flapper type valve assembly  34  generally including a valve housing or body  36  and a flapper member  38 . The flapper member  38  is pivotably mounted in the valve housing  36  upon a pin  50  and is movable between at least one open position ( FIG. 2A ) and at least one closed position ( FIG. 2B ) relative to a central, longitudinally extending bore  44  through the valve housing  36 . A valve opening device  57  is used to open the flapper member  38 . In the illustrated valve  32 , the valve opening device  57  is a reciprocating tubular member  58  movable downwardly into contact with the flapper member  38  to push it off of a valve seat  54  into an open position, as is known in the art. By maintaining a downward position of the tubular member  58 , whereby the tubular member  58  remains engaged with the flapper member  38  and is thus in an “engaged position”, the flapper member  38  is (at least temporarily) held in an open position, permitting fluid flow through the bore  44  and well tubing  14 , such as during normal operations.  
         [0017]     Still referring to  FIGS. 2A and 2B , to allow the conventional flapper member  38  to move from an open to a closed position, the tubular member  58  of the exemplary configuration is moved upwardly out of its engaged position. As the lower end  59  of the tubular member  58  moves above the valve seat  54 , the spring force of a spring  52  and/or the upward fluid flow through the tubing string  14  and bore  44  moves the flapper member  38  into a closed position. In  FIG. 2B , the flapper member  38  is shown yieldably urged about the pin  50  by the spring  52  into a closed position. In this position, the flapper member  38  of  FIG. 2  abuts the annular valve seat  54 , thus blocking upward flow of fluid through the bore  44  and tubing string  14  ( FIG. 1 ). These and other aspects of the illustrated safety valve are known in art. Further explanation of the components, arrangement and operation of conventional safety valves, such as the flapper type valve assembly  34 , and valve opening devices, such as the tubular member  58 , are more fully described in prior art patents and publication, such as U.S. Pat. Nos. 3,786,865, 3,786,866, 4,624,315, 5,127,476, 4,411,316, 4,356,867 and 4,723,606, each of which is hereby incorporated by reference herein in its entirety.  
         [0018]     The above description and further aspects of safety valves, such as the flapper type valve assembly  34 , and valve opening devices, such as the tubular member  58 , are in no way limiting upon the present invention or the appended claims. Moreover, the present invention is not limited to use with a flapper type valve, or tubular member type valve opening device, but can be used in connection with any suitable type of flow control device with, or without, any suitable type of valve opening device.  
         [0019]     Referring to  FIG. 3A , a primary hydraulic system  110  comprises a primary piston  112  and a primary hydraulic circuit  114 . Primary piston  112  has, in the embodiment shown, different upper and lower surface areas on which fluid pressure can bear. The lower surface of primary piston  112  is in operative communication with flow tube  59 , such that downward movement of the primary piston  112  causes downward movement of the flow tube  59 . Primary piston  112  may be in direct or indirect, hydraulic or mechanical, contact with the flow tube  59 .  
         [0020]     Primary hydraulic circuit  114  is in fluid communication with a pressure source (not shown) such as a pump and reservoir at the surface, and includes flowpaths  116 ,  118  to a port A and a port B, respectively. A primary valve  120  is disposed in flowpath  116  leading to port A. Primary valve  120  can be, for example, a shuttle valve, but is not restricted to that type of valve. Primary valve  120  does not regulate flow through port B. Primary hydraulic circuit  114  also includes a discharge flowpath  122  to discharge fluid from primary hydraulic circuit  114  to a region outside the circuit, such as into the annulus of a well bore. Discharge flowpath  122  may also discharge fluid to an internal chamber or return line to the surface or other contained volumes. Discharge flowpath  122  can be opened or closed by a vent valve  124 .  
         [0021]      FIG. 3B  shows a secondary hydraulic system  126  separate from primary hydraulic system  110 , except in some embodiments hydraulic systems  110 ,  126  could share a common source line to the pressure source. Secondary hydraulic system  126  may also share a common control line for valve operation. Alternatively, secondary hydraulic system  126  may be wholly or partially independent of the primary hydraulic system  110  to allow for full redundant operation. It should be noted for purposes of this application, redundant operation includes operation of the primary hydraulic system  110  and the secondary hydraulic system  126 , such that the secondary hydraulic system  126  can be operated to open flapper valve  38  without contribution from the primary hydraulic system  110 . Specifically, in the event of a failure of primary hydraulic system  110 , such as in the case of seal failure, the secondary hydraulic system is operated to maintain or re-establish downward pressure on the flow tube  59 , thus forcing flapper valve  38  to an open position.  
         [0022]     Secondary hydraulic system  126  comprises an upper piston  128 , a lower piston  130 , and a secondary hydraulic circuit  132 . Upper piston  128  is configured to be in abutting contact with lower piston  130 . A lock  134  is disposed in a housing  136  within the range of motion of upper piston  128 . The lock  134  may be any form of motion restricting device, such as a detent or a profile or such as a moveable latch. In any form, lock  134  restricts downward movement of the upper piston  128 . In a dormant position, the upper piston  128  lies above the lock  134 . To activate the secondary hydraulic system  126 , the upper piston  128  is moved beyond lock  134 . For example, lock  134  may comprise a profile having a constricted inner diameter that is rated to prevent downward movement of the upper piston  128  below a predefined pressure threshold. Alternatively, lock  134  may comprise a moveable latch that can be controlled either with a separate control line, electric or hydraulic, or via a run in tool to move the lock  134 .  
         [0023]     Secondary hydraulic circuit  132  is in fluid communication with a pressure source (not shown) such as a pump and reservoir at the surface, and includes upper and lower flowpaths  138 ,  140 , respectively. A secondary valve  142 , a shuttle valve for example, is disposed lower flowpath  140 . As stated above, the pressure source for the secondary hydraulic circuit  126  may be shared with the pressure source for the primary hydraulic system  110 . In such case, a lock  134  in the form of a profile would be rated to hold the position of the upper piston  128  above a pressure normally applied to the primary hydraulic system  110 . In other words, according to an embodiment, a same pressure is applied to both the primary piston  112  and the upper piston  128 . However, since the lock  134  is rated to hold above such pressure, only primary piston  112  is moved. Alternatively, the pressure sources for each hydraulic circuit may be independent of one another with separate control lines run to the piston  112  and pistons  128  and  130  respectively. Valves  120 ,  124 ,  142  can be controlled hydraulically, mechanically, or by using various other means well known in the art.  
         [0024]     The upper or shuttle piston  128  above the lower or secondary piston  130  has primary communication to system pressure. This shuttle piston  128  is merely one method of shifting the seals of the lower piston  130  into the piston bore of the housing  136 . It could be performed mechanically as well as hydraulically. For example, according to one embodiment, the shuttle piston  128  is separate from the lower piston  130  such that the travel of shuttle piston  128  is restricted to a down stop (not shown) and will not interfere with the operation of the secondary piston  130 , for example be restrict from movement across flow path  140 . Once the shuttle piston  128  shifts the seals of the secondary piston  130  into service, the previously dormant seals of the secondary piston  130  will assume hydraulic operation when valve  142  is activated to allow flow to path  140 .  
         [0025]     Primary hydraulic system  110  and secondary hydraulic system  126  are located in separate chambers within housing  36 . Although many configurations are possible, according to one embodiment, the primary hydraulic system  110  is located on an opposite side of the housing  36  compared to the secondary hydraulic system  126 . Both the primary piston  112  and the lower piston  130  are in operative communication with the flow tube  59 , such that downward movement of either the primary piston  112  or the lower piston  130  causes downward movement of the flow tube  59 . Further, lower piston  130  is independent or redundant of the primary piston  112 , such that downward movement of the flow tube  59  is effected either by primary piston  112  independent of any motion of lower piston  130  or by lower piston independent of any motion of primary piston  112 .  
         [0026]     In operation, primary hydraulic system  110  is used to control the motion of primary piston  112 . Vent valve  124  is normally closed and primary valve  120  is normally open. Pressurized fluid passing through flowpaths  116 ,  118  causes primary piston  112  to displace downward due to the differential areas. Specifically, the downhole force applied by the pressure in flowpath  116  to the top of primary piston  112  is greater than the uphole force applied by the pressure in flowpath  118  to the angled surfaces of primary piston  112 . In a typical application such as a safety valve, the downward displacement of primary piston  112  causes the lower end of primary piston  112  (or some other surface or hydraulic connection) to bear on a shoulder of a flow tube and displace the flow tube accordingly downward. The downward displacement of the flow tube opens a flapper valve to permit production of well fluids. If hydraulic pressure is removed from flowpaths  116 ,  118 , tubing pressure and a spring bias tend to drive the flow tube and primary piston  112  upward to allow the flapper valve to close, halting well production. In a closed position, when the primary piston is positioned fully upward, a metal static seal is effected between the piston chamber and the lower end of the piston.  
         [0027]     Primary hydraulic system  110  also allows primary piston  112  to be hydraulically driven upward if desired. That could be the case, for example, in the event of a failure somewhere in the primary hydraulic system. If vent valve  124  is opened and primary valve  120  is closed, then pressurized fluid can be directed into flowpath  118  only and will drive primary piston  112  upward while hydraulic fluid above primary piston  112  is discharged, into the well annulus for example, through discharge flowpath  122 . Valve  120  only shuts off flow from system pressure to path  116 . Path  116  and valve  124  are in series with the pressure on top of piston  112 . The shifting of valve  120  would only be used if you wanted to disable the primary piston ( i.e. should you have a seal leak). Then you would open valve  124  to allow system pressure or bore pressure to act to close the piston by pushing the fluid from the top of the piston to the annulus.  
         [0028]     To regain operational control of the safety valve, should operational control using primary hydraulic system  110  be lost, secondary hydraulic system  126  can be activated. With secondary valve  142  in a closed state, pressurized fluid passing through upper flowpath  138  will drive upper piston  128  downward, below lock  134 . As mentioned above, this movement may be effected either by exceeding the rated pressure threshold of a profile against the upper piston  128 , or via movement of a mechanical lock through a control or separate run in operation, or by other methods known in the art. According to one embodiment, lock  134  also prevents upward movement of upper piston  128  once secondary hydraulic system  126  is activated, such as shifting to far upward and uncovering the hydraulic seal. According to another embodiment there is a down stop (not shown) for upper piston  128 , for example to restrict movement past flowpath  140 . The downward motion of upper piston  128  drives lower piston  130  downward. Opening secondary valve  142  allows pressurized fluid into lower flowpath  140 , which further drives lower piston  130  downward. Lower piston  130  controls the motion of the flow tube in place of primary piston  112  in a similar manner.  
         [0029]     The advantages of the present invention include convenient methods that allow for redundant secondary hydraulics to control operation of a safety valve. These methods can be employed in a cost effective and efficient manner, providing an additional fail safe mode of operation.  
         [0030]     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.