Abstract:
A control system for a Subsurface Safety Valve (SSSV), includes an actuating piston mounted in a housing with at least one seal and connected to the SSSV. The actuating piston having a first end and a second end, the first end in fluid communication with a control line; a primary pressure reservoir in fluid communication with the second end of the actuating piston, the reservoir configured to contain a fluid under an amount of pressure selected to act against a prospective hydrostatic pressure expected in the control line based upon the selected position of the control system in a downhole environment. An equalizing piston in fluid communication with both the control line and with the second end of the actuating piston, the equalizing piston remaining in a closed position during shifting of the actuating piston with pressure applied or removed from the control line, the equalizing piston movable to an open position upon a control system failure that reduces pressure in the primary reservoir to below a threshold value; and a condition sensing and chemical injection assembly in fluid communication with the primary reservoir. A method for operating a control system for a Subsurface Safety Valve (SSSV).

Description:
BACKGROUND 
     Safety valves are ubiquitous in the downhole industry. Consequently, control systems number aplenty as well. In each case, the primary concern is that in the event of a failure of any part of the control system, the valve will either remain in or automatically proceed to a “safe” position. This may be open or closed depending upon the particular configuration. 
     Regardless of the number of presently available systems however, the art is generally receptive to alternative configurations with differing attributes and enhanced capabilities. 
     BRIEF DESCRIPTION 
     A control system for a Subsurface Safety Valve (SSSV), includes An actuating piston mounted in a housing with at least one seal and connected to the SSSV, the actuating piston having a first end and a second end, the first end in fluid communication with a control line; a primary pressure reservoir in fluid communication with the second end of the actuating piston, the reservoir configured to contain a fluid under an amount of pressure selected to act against a prospective hydrostatic pressure expected in the control line based upon the selected position of the control system in a downhole environment; an equalizing piston in fluid communication with both the control line and with the second end of the actuating piston, the equalizing piston remaining in a closed position during shifting of the actuating piston with pressure applied or removed from the control line, the equalizing piston movable to an open position upon a control system failure that reduces pressure in the primary reservoir to below a threshold value; and a condition sensing and chemical injection assembly in fluid communication with the primary reservoir. 
     A method for operating a control system for a Subsurface Safety Valve (SSSV) includes raising pressure in the control line in the system of claim  1  to a selected maximum working pressure; holding the maximum working pressure in the line and monitoring for pressure fall off; concluding that 1) the control system is operational if pressure is maintained for a selected period of time or that 2) the control system is not operational if pressure is not maintained for the selected period of time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a schematic representation of a safety valve control system with the valve in a closed position and the control system operational; 
         FIG. 2  is the system of  FIG. 1  illustrated with the valve in an open position and the control system operational; 
         FIG. 3  is the system of  FIG. 1  in a tripped condition where control line fluid is communicated to a primary reservoir; 
         FIG. 4  is the system of  FIG. 1  illustrated in a tripped condition with the condition and chemical injection assembly open; 
         FIG. 5  is an enlarged view of an alternate embodiment of the condition sensing and chemical injection assembly illustrated in the area of  FIG. 1  circumscribed at  5 - 5 ; and 
         FIG. 6  is the view of  FIG. 5  in an actuated condition. 
     
    
    
     DETAILED DESCRIPTION 
     The control system C is illustrated in  FIG. 1 . An actuation piston  10  is schematically illustrated as having an extension tab  12  on which a spring  14  acts to push the piston  10  to the position shown in  FIG. 1 . The tab  12  is connected to a flow tube (not shown) which in turn, when pushed down, swings a flapper (not shown) so as to open the passageway in a wellbore. The structure of the subsurface safety valve (SSSV) is not illustrated because it is common and well-known. The invention lies in the control system for the SSSV as opposed to the construction of the SSSV components themselves. Those skilled in the art will appreciate that the SSSV has a housing which can include many of the components of the control system C. The control system C is accessed from the surface of the wellbore by a control line  16  which runs from the surface of the wellbore to fluid communication with conduits  20  and  22 . Conduit  22  opens up to top surface  24  of piston  10 . Seal  26  prevents fluid in the control line  16  from bypassing around the piston  10 . Another seal  28  is adjacent the lower end of the piston  10  near surface  30 . Piston  10  has a passageway  32  which extends from surface  30  to an outlet  34  between seals  26  and  36 . As such, the portion of piston  10  between seals  36  and  28  is exposed to the pressure in the housing of the SSSV as the piston  10  moves to a SSSV open position or an SSSV closed position. 
     A pressurized primary reservoir  38  contains a pressurized gas, preferably an inert gas such as nitrogen, above a level of hydraulic fluid  40  which communicates through a conduit  42  in turn to conduits  44  and  46 . Conduit  44  allows the fluid  40  to exert a force against surface  30  of piston  10 . The pressure in conduit  44  is communicated through passageway  32  to the area between seals  26  and  36 . However, the pressure thus communicated through passageway  32  does not act to operate piston  10  during normal operations. In essence, passageway  32  constitutes a pressure leak path to ensure that the control system C puts the SSSV in a closed position if a failure occurs at seal  36 . 
     A secondary reservoir  48  communicates with a surface  50  of an equalizing piston  52 . A seal  54  isolates secondary reservoir  48  from conduit  20  in the position shown in  FIG. 1 . Seal  56 , in the position shown in  FIG. 1 , isolates conduit  20  from conduit  46 . Between conduit  46  and piston  52 , as shown in  FIG. 1 , there is an enlarged bore  58 . There&#39;s also an enlarged bore  60  below seal  54  in the position shown in  FIG. 1 . The purpose of the enlarged bores  58  and  60  is to permit bypass flow around the seals  54  and  56  after piston  52  shifts. Referring to  FIG. 3 , when the equalizing piston  52  shifts due to failure of a variety of different components as will be explained below, seal  56  no longer seals conduit  20  from conduit  46 , thus allowing pressure from the control line  16  to equalize into conduit  44  and, hence, at the bottom  30  of the piston  10 . It should be noted that seal  54  no longer seals reservoir  48  because it has moved into enlarged bore  60 . When this happens, the piston  10  is in pressure balance and the return spring  14  can push the tab  12  upwardly, moving the piston  10  from the position shown in  FIG. 2  where the SSSV is open, to the position in  FIG. 3  where the SSSV is closed. It is to be appreciated that the particular configuration of the equalizing piston  52  and associated components is supplied for example only and that other arrangements for the system such as a ratcheting configuration that prevents equalizing piston  52  from repositioning after a trip condition are also contemplated for use in this disclosure. The ratcheting configuration as well as other arrangements in the tool are known from commercially available product families H82706, H82699, H82672 commonly referred to as the Neptune™ Performance series nitrogen-charged subsurface safety valve and available from Baker Hughes Incorporated Houston Tex. 
     The normal operation to open the SSSV using the control system C requires nothing more than applying pressure in the control line  16 . It should be noted that the pressure in the primary reservoir  38  is above the hydrostatic pressure in the control line  16  from the hydraulic fluid therein in order to counteract the force presented thereby. In one embodiment, and arbitrarily, the value of the pressure in the primary reservoir  38  can be 500 psi above the anticipated hydrostatic pressure in the control line  16  at the depth at which the SSSV will be installed. Those skilled in the art will appreciate that the charges of pressure in primary reservoir  38 , as well as secondary reservoir  48 , need to be determined at the surface before the SSSV is installed. The pressure in the secondary reservoir  48  is to be below the prescribed pressure in the primary reservoir. In one embodiment and selected for convenience, the pressure used in the secondary reservoir  48  is 50 psi less than the anticipated control line hydrostatic pressure. The purpose of the primary reservoir  38  is to offset the hydrostatic force on piston  10  from control line  16 . Piston  52  is normally under a pressure imbalance which is caused by the pressure difference between reservoirs  38  and  48 . The hydrostatic or applied pressure in conduit  20  has no net force impact on piston  52 . 
     Finally the reader&#39;s attention is directed to the bottom left corner of the figures where a condition sensing and chemical injection assembly  70  is illustrated. The assembly will be available for use at any time for condition sensing and under certain failure conditions of the control system C, for chemical injection repurposing of the control system C. The assembly  70  is to be positioned within the control system C to fluidly communicate between the primary reservoir  38  and the tubing components of the SSSV outside of the control system itself. The assembly comprises one or more burst disks  72 , a one-way check valve  74  and an atmospheric chamber  76  between the one or more burst disks and the check valve. It is to be noted that in some embodiments atmospheric pressure may also be maintained between any two or more burst disks as well as between the burst disk nearest the check valve and the check valve itself. The check valve  74  comprises a spring  78  and a poppet head  80  that will seat in a seat  82  under influence of the spring  78  when control line pressure is not exceeding the spring force of spring  78  plus tubing pressure, to which the poppet head  80  is exposed at a side opposite the control line  16 . The check valve  74  is openable based upon control line pressure being above the spring force plus tubing pressure (after the one or more burst disks have burst). The check valve  74  will reseat upon a control line pressure below tubing pressure and spring force. 
     It is to be understood that one burst disk  72  is sufficient for functionality of the assembly  70  but more than one will also work well and may provide for additional reliability in function. The atmospheric chamber  76  is important to ensure that the burst disk(s) burst ratings will be closely related to actual pressure differential numbers in situ. Were it not for the atmospheric chamber  76 , the rating of the burst disk(s) would be subject to the variability of the tubing pressure (which very well might be above the control line maximum working pressure). With the atmospheric chamber  76 , burst disks  72  may be rated to burst at the maximum working pressure of the control line, which rating will be close to constant. The bursting of the one or more burst disks will itself provide one of the condition indicators that is a benefit of the invention. More specifically, with the burst disk(s) rupturing at the maximum working pressure of the control line, a condition sensing function is realized. This will be better understood in the discussion hereunder. 
     The principal components of the control system having been described, its normal operation will now be reviewed. In order to actuate the SSSV from the closed position shown in  FIG. 1  to the open position shown in  FIG. 2 , pressure is increased in control line  16 . It should be noted that until the pressure in the control line  16  is elevated, the piston  10  is subject to a net unbalanced upward force from the pressure in primary reservoir  38  since it is 500 psi higher than the control line  16  hydrostatic pressure. However, upon sufficient elevation of pressure in the control line  16 , to a level of approximately 2000 psi plus the primary nitrogen charge pressure in primary reservoir  38 , a downward differential force exists across piston  10  which is great enough to overcome the applied upward forces resulting from the pressure in primary reservoir  38 , as well as the force of the spring  14 . When that occurs, the piston  10  moves downwardly, taking with it the flow tube (not shown), which in turn allows the spring-loaded flapper (not shown) to be rotated downwardly and out of the flowpath, thus opening the SSSV. The final position with the SSSV in the open position is shown in  FIG. 2 . As seen in  FIG. 2 , the piston  10  has traveled downwardly against the bias of spring  14  and tab  12 , which is engaged to the flow tube, has moved the flow tube (not shown) down against the flapper to rotate the flapper (not shown) about 90° from its closed to its open position. 
     The closure of the SSSV occurs normally through a reversal of the procedure outlined above. The pressure in the control line  16  is reduced. When the pressure is sufficiently reduced, a net unbalanced upward force occurs on piston  10  due to the pressure in primary reservoir  38  acting on surface  30 . This force, in combination with the force of spring  14 , becomes greater than the hydrostatic force from the fluid column in the control line  16 , thus allowing the piston  10  to move back upwardly to its position shown in  FIG. 1 . Reversal of movement occurs with respect to the flow tube and the flapper, allowing the SSSV to move to a closed position. It should be noted at this time that passageway  32  is a leak path whose purpose will be explained below. Although the pressure exerted from the gas in primary reservoir  38  acting on hydraulic fluid in lines  42  and  44  communicates with passage  32 , the existence of passage  32  has no bearing on the net upward force exerted on piston  10 . Accordingly, when seals  26  and  36  are in proper working order, there is simply a dead end to passageway  32  such that surface  30  of piston  10  acts as if it were a solid surface, making the net force applied by gas pressure in primary reservoir  38  act, through an intermediary fluid, on the full diameter of surface  30  during normal operations. 
     Potential problems can occur in the control system when the SSSV is in the closed position shown in  FIG. 1  or when it is in the open position as shown in  FIG. 2 . These are detailed in U.S. Pat. No. 6,109,351, the entirety of which is incorporated by reference. 
     With more particular relevance to the present disclosure, the assembly  70  provides for two distinct benefits in the control system C as described above or in other control systems as well. Application of the disclosure below to other control systems will be understood by those of skill in the art following a thorough reading of the description below with reference to the figures. The benefits, as noted above are, 1) a condition sensing capability and 2) a chemical injection capability. The condition sensing capability employs maximum working pressure on the control line. The actual pressure can be whatever the design pressure of the control line  16  is since actual pressure is immaterial to the functionality of the configuration. The one or more burst disks  72  however will be rated to burst at substantially the same pressure as maximum working pressure of the control line  16 . When an operator desires to check the condition of the SSSV and the control system C, pressure is raised within the control line to the maximum working pressure of the control line  16 . If pressure can be maintained at maximum working pressure for a selected period of time, for example a few minutes, then the Control system C is functional. This is known from this exercise because if the pressure is maintainable, the control system has not communicated the control line to the primary reservoir portion of the system. Without this communication, control line pressure does not reach the one or more burst disks and hence cannot rupture the one or more burst disks. This provides a simple and rapid confirmation that the control system is still in working order. Conversely, if the system has indeed tripped meaning that control line pressure is communicated to the primary reservoir portion of the system, the one or more burst disks  72  will rupture at the control line maximum working pressure level. More specifically, in order for the one or more burst disks  72  to rupture, control line pressure must already have been communicated to the burst disk, which indicates a “tripped control system”, a failure mode that results in control line pressure at both ends of the piston  10  so that spring  14  will close the SSSV. This condition is fully described in the above incorporated patent. If the system is tripped then raising control line pressure to maximum working pressure will result in the pressure at the one or more bursts disks being at the same maximum working pressure. If, as noted is the case, the one or more burst disks are rated to rupture at the maximum working pressure of the control line, they will rupture when pressure reaches that value. Once the one or more disks rupture, pressure in the control line will begin to fall. In this situation, it will not be possible to maintain the maximum pressure for the prescribed period of time, thereby providing the operator with a positive indication that the control system C has tripped. In the event that the above described testing for condition has been undertaken in relation to an SSSV not moving scenario, the operator can be confident that either the valve is physically stuck with scale, paraffin, etc. or the control system has tripped. If the valve is physically stuck, interventions would then be indicated to exercise the SSSV. If the system is tripped however, different actions would be indicated. In one desirable iteration, the control system as described is duplicated in an entirely redundant secondary control system and accordingly upon a confirmation of a tripped control system, the secondary control system would be used to attempt actuation of the SSSV without the need for a separate run of tools to exercise the SSSV. The configuration as described avoids separate runs to determine the cause of a valve not moving condition, reducing the total number of interventional activities to those situations where they are actually needed. 
     Another aspect of the invention described herein is the repurposing of the control system C to be used as a chemical injection system if indeed the test described above identifies a tripped condition (a control system failure). Heretofore, a control system failure simply meant that the control system had no continuing utility for the operator and a backup system would be utilized. Configured as taught herein however, the control system may be further operated as a chemical injection system. Moreover, the chemicals injected by the system will be placed more advantageously than prior art methods. In particular, where a tripped condition has occurred and the one or more burst disks have burst as described above, the hydraulic fluid from the control system will leak into areas surrounding the components of the SSSV behind the flow tube (locations will be understandable to one of skill in the art). Because the control system has the ability to supply fluid to that location through the burst disks and check valve  74  greater chemical action of a chemical injection fluid would be realized. In particular, the control line fluid is swapped out for chemical injection fluid. Normally this would be done by simply pushing the control fluid past the check valve and continuing to pump fluid until a sufficient amount of the chemical injection fluid has reached the SSSV. The configuration as such, renders a heretofore useless system (having been tripped) a newly useful system in a repurposed way. Because of the location of the supply of chemical injection fluid as noted above, the result is even better than prior art such as chemical injection fluid run on a tubing string of some kind since the injection fluid goes directly to the components of the valve that will most benefit from its presence. 
     Referring to  FIGS. 5 and 6 , an alternate embodiment of the condition sensing and chemical injection assembly is illustrated. The illustrations are similar to  FIGS. 1-4  but for the lower left corner of each figure where the condition sensing and chemical injection assembly may be viewed. The assembly  170  of  FIGS. 5 and 6  replaces assembly  70  of  FIG. 1 . Some of the components are similar and hence are given  100  series numerals of those found in  FIGS. 1-4 . These include one or more burst disks  172 , check valve  174 , atmospheric chamber  176 , spring  178 , poppet head  180 , and seat  182 . Differing from  FIGS. 1-4  however, is seal insert  200  which provides for an even more reliable atmospheric chamber  176  between the one or more burst disks  172  and the balance of the assembly  170  (this embodiment also may include additional atmospheric chambers between any two of the burst disks. The seal insert  200  comprises a piston like body  202  supporting a seal  204  such as an o-ring. The o-ring  204  seals against an inside diameter of a housing  206  of the assembly  170 . The seal insert  200  provides for a movable positive seal in a first position and in a second position, illustrated in  FIG. 6 , where the housing  206  has a larger inside diameter area  208  that is too large for the seal insert  200  to seal. Hence, fluid may flow around the seal insert  200  and act upon check valve  174  as described in the embodiment described above. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.