Patent Publication Number: US-10316603-B2

Title: Failsafe valve system

Description:
BACKGROUND 
     In a variety of subsea well applications, a subsea test tree is deployed into subsurface equipment to enable subsea well control during completion operations, flow testing operations, intervention operations, or other subsea well operations performed from a surface facility, such as a floating vessel. For example, the subsea test tree may be used within a subsea blowout preventer to control fluid flow. Depending on the subsea operation, various types of well equipment, e.g. coiled tubing or wireline, may be deployed through the subsea test tree via an interior passageway. The subsea test tree also comprises several valves, including valves which fail to a closed position to secure the wellbore if hydraulic control pressure is lost. However, if the hydraulic control pressure is lost when the well equipment is disposed in the interior passageway, difficulties can arise with respect to shearing equipment, e.g. coiled tubing, to enable closure of the failsafe valve. Some failsafe valves are in the form of ball valves which close under the force of a mechanical spring. However, the mechanical spring tends to provide insufficient force for shearing coiled tubing and other types of equipment. 
     SUMMARY 
     In general, a system and methodology facilitate failsafe closure of a valve used in, for example, a subsea test tree. The system and methodology enable sufficient application of force to combine the failsafe valve with a cutter able to cut through coiled tubing and other well equipment. In this embodiment, a valve is combined with a cutter oriented to sever well equipment passing through an interior passage of the valve. The valve is operatively coupled with an actuation system having an actuator piston which controls cutting and valve closure. The failsafe valve and the cutter are shifted to an open position by applying pressure in a control fluid chamber to shift the actuator piston. However, the actuator piston, and thus the valve and cutter, are biased toward a closed position via pressure applied in a pressure chamber and a gas precharge chamber. The combined pressure ensures adequate force for shearing of the well equipment and closure of the valve when hydraulic control pressure is lost. In some applications, additional closing force may be selectively provided to the actuator piston. 
     However, many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate the various implementations described herein and are not meant to limit the scope of various technologies described herein, and: 
         FIG. 1  is a schematic illustration of an example of a subsea test tree having a failsafe valve coupled with an actuation system, according to an embodiment of the disclosure; 
         FIG. 2  is a cross-sectional view of an example of an actuation system coupled with a failsafe valve, according to an embodiment of the disclosure; 
         FIG. 3  is a cross-sectional view of an example of an actuation system for use with a failsafe valve, according to an embodiment of the disclosure; and 
         FIG. 4  is a cross-sectional view of another example of an actuation system for use with a failsafe valve, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of some embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present disclosure generally relates to a system and methodology which facilitate failsafe closure of a valve used in, for example, a subsea test tree. The subsea test tree may be deployed into subsea equipment, such as a blowout preventer, wellhead, and/or Christmas tree. Depending on the application, the subsea test tree may comprise a variety of hydraulically controllable valves able to facilitate various completion operations, flow testing operations, intervention operations, or other well related operations. Additionally, the subsea test tree comprises at least one failsafe valve which fails to a closed position to prevent unwanted flow of well fluids through the subsea test tree in the event hydraulic control is lost. In some applications, a plurality of failsafe valves may be utilized, for example, below a latch connector. 
     As described in greater detail below, at least one of the failsafe valves is coupled to an actuator system which substantially increases the force applied for valve closure. This type of system provides the failsafe valve with substantial cutting capability so that various types of well equipment, e.g. coiled tubing, wireline, slick line, may be sheared during failsafe closure of the valve. According to an embodiment, the system and methodology enable sufficient application of force to combine the failsafe valve with a cutter able to cut through the well equipment extending along an interior passage of the subsea test tree. 
     In this embodiment, the valve is operatively coupled with an actuation system having an actuator piston which can be actuated with sufficient power to ensure both cutting and valve closure. The failsafe valve and the cutter may be shifted to an open position by applying pressure in a control fluid chamber to shift the actuator piston. However, the actuator piston, and thus the valve and cutter, are biased toward a closed position. For example, the valve and cutter may be biased to the closed position via pressure applied cumulatively in a pressure chamber and a gas precharge chamber. The combined closure pressures ensure adequate force for shearing of the well equipment and closure of the valve when hydraulic control pressure is lost. In some applications, additional closing force may be selectively provided to the actuator piston. 
     The valve and cutter combination may be constructed with a variety of valve types and also a variety of cutter types. In some embodiments, the valve and the cutter may be separate units which are both operable by the actuator piston. However, the cutter also may be combined with the valve. For example, the cutter may be in the form of a cutter edge mounted to, or formed along, an edge of a ball valve or a spherical gate cutter or gate valve. 
     Referring generally to  FIG. 1 , an example of a well system  20  is illustrated. In this embodiment, the well system  20  comprises a subsea test tree  22  which may be deployed into suitable subsea equipment, such as a blowout preventer, wellhead, and/or Christmas tree. The subsea test tree  22  comprises an interior passage  24  through which well equipment  26 , e.g. coiled tubing  28 , may be deployed. Depending on the parameters of a given application, the subsea test tree  22  may comprise a variety of components and the embodiment illustrated in  FIG. 1  is provided for purposes of explanation. Additional and/or other components may be combined into the subsea test tree  22 . 
     In the embodiment illustrated, subsea test tree  22  comprises an upper valve section  30  disposed above a latch connector  32 . By way of example, the upper valve section  30  may comprise a plurality of valves, such as a bleed off valve  34  and a retainer valve  36  which may be hydraulically controlled via hydraulic control lines  38 . In some applications, a lubricator valve  40  also may be coupled with the upper valve section  30 . It should be noted that the number, arrangement, and type of valves disposed in upper valve section  30  may vary depending on the parameters of a given subsea operation. 
     Below latch connector  32 , the subsea test tree  22  may comprise a lower valve section  42  having at least one failsafe valve  44  operatively coupled with an actuation system  46 . The actuation system  46  automatically shifts the failsafe valve  44  to a closed position to block fluid flow along interior passage  24  in the event hydraulic control over the subsea test tree  22  is lost. For example, if the subsea test tree  22  is separated at latch connector  32 , the actuation system  46  is able to automatically close the failsafe valve  44  and prevent unwanted flow through interior passage  24 . 
     In this example, the failsafe valve  44  is combined with a cutter  48  which is oriented to cut through the coiled tubing  28  or other well equipment  26  which may be disposed along interior passage  24  and through the failsafe valve  44 . By way of example, the cutter  48  may comprise a cutting edge formed of a hardened steel material, composite material, or other suitable material. The cutting edge of cutter  48  is able to shear through well equipment  26  when failsafe valve  44  is closed with sufficient force. 
     The failsafe valve  44  may be constructed in a variety of configurations. For example, the failsafe valve  44  may be in the form of a ball valve  49  or spherical gate valve. The failsafe valve  44  may be operatively coupled with actuation system  46  via an actuation link  50 . The actuation link  50  may be a mechanical link, e.g. an actuator arm, or a fluid link, e.g. a flow passage, able to forcibly drive valve  44  to the closed position when directed by actuation system  46 . In this example, the actuation system  46  also is coupled with a subsea control system  52 , e.g. a subsea electrohydraulic control system, which provides the pressure for operation of actuation system  46  with the desired cutting and closing capability. By way of example, the subsea control system  52  may be configured to enable selective pressurization of a control line to at least an annulus pressure as described in greater detail below. In some applications, the subsea control system  52  comprises a pressure compensated chamber and/or a stored pressure volume pressurized to a desired pressure level, e.g. a pressure level in the range from 5000 psi to 10,000 psi. 
     It should be noted that other components and features also may be located below latch connector  32 . In some embodiments, an additional valve  54 , e.g. a flapper valve, may be positioned below latch connector  32 , e.g. between actuation system  46  and latch connector  32 . The flapper valve  54  also may be in the form of a failsafe closure valve. 
     Referring generally to  FIG. 2 , an embodiment of actuation system  46  is illustrated in cross-section as attached to failsafe valve  44 . In this example, the failsafe valve  44  is in the form of ball valve  49  although the valve  44  may be a spherical gate valve or other suitable valve. Additionally, the valve  44  comprises an interior passage  56  which effectively is a continuation of the interior passage  24 , passing through the subsea test tree  22 , when passage  56  is aligned with passage  24 . The valve  44  also is combined with cutter  48  which may be in the form of a cutting edge positioned along an edge of the ball valve  49  adjacent interior passage  56 . 
     In this embodiment, the actuation system  46  comprises an actuator piston  58  coupled to the failsafe cutter valve  44  via hydraulic or mechanical link  50 . The actuator piston  58  is in fluid communication with a pressure chamber  60 , a gas precharge chamber  62 , a low-pressure chamber  64  (e.g. an atmospheric pressure chamber or low-pressure gas charged chamber), and a control fluid chamber  66 . The actuator piston  58  is slidably mounted within an actuator system housing  68  and is configured to form the various chambers  60 ,  62 ,  64 ,  66  along the interior of housing  68 . 
     In this example, the control fluid chamber  66  is pressurized to move the actuator piston  58  and thus the cutter valve  44  to an open position. In other words, pressurizing hydraulic fluid in control fluid chamber  66  with sufficient pressure causes the actuator piston  58  to move upwardly with respect to housing  68  in the example illustrated in  FIG. 2 . However, the pressure chamber  60  and the gas precharge chamber  62  cooperate to bias the actuator piston  58  and the cutter valve  44  in an opposite direction toward a closed position. The pressure chamber  60  may be coupled with subsea control system  52  which supplies the pressure chamber  60  with fluid at an annulus pressure or a higher pressure. 
     Actuator piston  58 , pressure chamber  60 , and gas precharge chamber  62  are configured such that the pressures in pressure chamber  60  and gas precharge chamber  62  are cumulative. The combined pressures of pressure chamber  60  and gas precharge chamber  62  can be used to shift actuator piston  58  and thus failsafe valve  44  with sufficient force to cut through well equipment  26  positioned along interior passage  24  and to thus close valve  44 . When failsafe valve  44  is in the closed position, fluids, e.g. well fluids, are blocked from flowing upwardly along interior passage  24 . 
     With additional reference to  FIG. 3 , a specific embodiment of actuation system  46  is illustrated. In this embodiment, the actuator piston  58  is slidably mounted between an interior tubular member  70 , defining a portion of interior passage  24 , and the surrounding housing  68 . In some applications, the tubular member  70  may be positioned within housing  68  via at least one suitable mounting structure  72  of housing  68 . The slidably mounted actuator piston  58  also may be sealed with respect to both the interior tubular member  70  and the surrounding housing  68  (with or without mounting structure  72 ) via a plurality of seals  74 , e.g. O-ring seals. Seals  74  also may be utilized between other components, such as between mounting structure  72  and other portions of housing  68 . 
     In the example illustrated, actuator piston  58  comprises an expanded region  76  which seals against an interior of the mounting structure  72  via at least one seal  74  to separate pressure chamber  60  and gas precharge chamber  62 . The actuator piston  58  also comprises a larger diameter expanded region  78  which similarly seals against an interior surface of housing  68  via at least one seal  74  to separate gas precharge chamber  62  and low-pressure chamber  64 . It should be noted low-pressure chamber  64  is not pressurized in this embodiment. Depending on the embodiment, chamber  64  may be an atmospheric chamber or a low-pressure gas charged chamber. The actuator piston  58  further comprises an additional expanded region  80  which seals against an interior surface of housing  68  via at least one seal  74  to separate the chamber  64  from control fluid chamber  66 . In this example, the diameter of expanded region  78  is larger than the diameter of expanded region  76  to facilitate the cumulative application of force due to pressures in pressure chamber  60  and gas precharge chamber  62 . The diameter of expanded region  78  also may be larger than the diameter of the additional expanded region  80 . It should be noted the actuation system  46  is illustrated as placed in a wellbore such that an annulus  82  is formed between the actuation system  46  and the surrounding wellbore wall. 
     The structure of actuator piston  58  and the various chambers  60 ,  62 ,  64 ,  66  enable the application of substantial closing and cutting force to failsafe valve  44  when the pressurized control fluid is bled from control fluid chamber  66 . In the illustrated example, the pressure chamber  60  may be placed in fluid communication with subsea control system  52  via a suitable passageway or passageways  84 . In some applications, passageways  84  comprise gun drilled holes formed in actuation system  46 . Additionally, the control fluid chamber  66  may be coupled with a control line  86  which enables selective pressurization of control fluid chamber  66  to shift the actuator piston  58  and the cutter valve  44  to an open position. The open position allows movement of fluid and/or well equipment  26 , e.g. coiled tubing  28 , through the interior passage  24 . 
     The control line  86  may be coupled with subsea control system  52  and/or with a pressure control system  88 , e.g. a hydraulic pump system, which may be located at the surface or at another suitable position. The pressure control system  52  and/or  88  is operated to selectively provide hydraulic fluid under pressure to control fluid chamber  66 . The pressurized hydraulic fluid is used to drive piston  58  against the bias of chambers  60 ,  62  so as to shift the actuator piston  58  and valve  44  to the open position. 
     In some applications, pressure control system  88  may be part of or coupled with pressure supply equipment deployed along interior passage  24 . In this type of application, the pressure supply equipment may be conveyed down interior passage  24  and used to monitor and refill the control fluid chamber  66  and/or to control the valve  44  and cutter  48  directly. The control line  86  may be appropriately routed to an interior or exterior of the actuation system  46  or may be drilled or otherwise formed within components of actuation system  46 . 
     It should be noted that pressure control system  88  may comprise an individual system or a plurality of cooperating systems used to selectively apply pressurized fluid to one or more regions of actuation system  46 . For example, the pressure control system  88  also may comprise suitable equipment, e.g. a fluid pumping system  90 , so as to enable controllable increasing of the pressure in annulus  82  while also providing other controlled sources of pressure. In some applications, increased pressure in annulus  82  may be used to pressurized chamber  66  and/or other chambers along piston  58 . However, dedicated control lines also may be used to supply pressure from system  88  to desired chambers of actuation system  46 . 
     In some embodiments, for example, the pressure systems  52  and/or  88  may be coupled to gas precharge chamber  62  via an additional control line  92 . In the event pressurized gas is lost from gas precharge chamber  62  (or the pressure of gas in chamber  62  is insufficient to close valve  44 ) increased pressure can be provided to chamber  62  via the corresponding pressure system and control line  92 . It should be noted that control line  92  may be routed through or along the actuation system  46  and subsea test tree  22  via a variety of techniques. 
     The gas precharge chamber  62  may be pre-charged with various fluids. By way of example, the gas precharge chamber  62  may be pre-charged with nitrogen to a desired pressure. The desired pressure may vary depending on the application, available annulus pressure, arrangement of pressure system  88 , depth of application, or other parameters. In some applications, an additional spring member  94 , e.g. a coil spring, also may be added to facilitate movement of actuator piston  58  and valve  44  in a closing direction, as illustrated in  FIG. 4 . By way of example, the spring member  94  may be mounted within gas precharge chamber  62  in a position acting between housing  68 , e.g mounting structure  72 , and large diameter expanded region  78  to provide a closing bias even if gas in chamber  62  is lost. Depending on the configuration of subsea test tree  22 , the actuation system  46  also may comprise a variety of connection related components  96  which are configured and oriented to facilitate coupling of the actuation system  46  with a next adjacent component of subsea test tree  22 . 
     In operation, the subsea test tree  22  is deployed to a subsea location and positioned within the corresponding subsea equipment, e.g. blowout preventer. According to an embodiment, the pressure chamber  60  and subsea control system  52  are in fluid communication via control line  84 . The subsea control system  52  is used to pressurize the control line  84  and the pressure chamber  60  to at least annulus pressure via a suitable technique. For example, the subsea control system  52  may comprise a pressure compensated chamber and/or a stored pressure volume to provide the desired pressure to chamber  60  via control line  84 . The pressure in annulus chamber  60  and the pressure in gas precharge chamber  62  cumulatively act against actuator piston  58  and provide cumulative forces biasing actuator piston  58  and failsafe valve  44  to a closed position with respect to interior passage  24 . 
     However, the valve  44  may be opened via pressure selectively applied to control fluid chamber  66 . The control fluid chamber  66  may be monitored and refilled via various techniques. For example, the control fluid chamber  66  may be monitored and refilled via control line  86  routed to pressure control system  88  at a surface location or via control line  86  routed to the subsea control system  52 . In some applications, pressure may be supplied to control fluid chamber  66  via annulus  82 . 
     In some embodiments, additional shearing capability may be provided by using pressure control system  88  to increase the pressure in control line  84  and thus in pressure chamber  60 . In general, however, the control line  84  is routed to subsea control system  52  which maintains the pressure chamber  60  at an annulus pressure or at a pressure higher than annulus pressure. Pressure boosting is further accomplished by having the pressure of gas precharge chamber  62 , e.g. a nitrogen chamber, acting cumulatively with pressure chamber  60  while atmospheric chamber  64  provides little or no resistance. Additionally, some embodiments may utilize the control line  92  or control lines coupled to the gas precharge chamber  62  and/or the pressure chamber  60 . The control line(s)  92  may be coupled with pressure control system  88  to enable a selective increase in pressure in the gas precharge chamber  62  and/or pressure chamber  60  to further enhance the shearing capability of cutter valve  44 . Supplemental biasing components, such as spring member  94 , may be used to provide increased valve closing bias in the event gas, e.g. nitrogen, is lost from gas precharge chamber  62 . 
     The size and structure of the subsea test tree  22 , failsafe valve  44 , and actuation system  46  may be adjusted according to the parameters of a given application. For example, valve  44  may comprise a variety of ball valves, gate valves, or other valves which may be coupled to the actuation system  46  in a manner which ensures failsafe operation to prevent unwanted fluid flow through interior passage  24  in the event hydraulic control over the subsea test tree  22  is lost. The actuation system  46  as well as the linkage  50  between the actuation system  46  and valve  44  also may be adjusted to accommodate the specifics of a given application. For example, the size and configuration of the actuator piston and the corresponding chambers may be adjusted to provide the desired relative pressures and biasing forces acting on actuator piston  58  and valve  44 . The subsea test tree  22  also may be used with various types of subsea equipment in many types of operations. 
     Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.