Patent Publication Number: US-6659184-B1

Title: Multi-line back pressure control system

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a system for controlling downhole well tools to produce hydrocarbons from a wellbore. More particularly, the invention relates to a back pressure control system providing safe operation in multiple hydraulic control lines. 
     Downhole well tools control, select and regulate the production of hydrocarbon fluids and other fluids produced downhole from subterranean formations. Downhole well tools such as sliding sleeves, sliding side doors, interval control lines, safety valves, lubricator valves, chemical injection subs, and gas lift valves are representative examples of such tools. Well tools are typically controlled and powered from the wellbore surface by pressurizing hydraulic lines which extend from a Christmas Tree or other wellhead and into the wellbore lower end. 
     Dual pressure barriers in hydraulic lines are preferred to prevent hydraulic line failure during a wellbore catastrophic event. Dual pressure barrier systems have an active and a passive barrier. The active barrier typically comprises a valve located at the Christmas Tree or wellhead, and the passive barrier typically comprises a check valve located in the hydraulic line below the wellhead. The check valve restricts fluid flow in one direction as the hydraulic fluid, chemicals or other fluids are pumped downhole into the hydraulic line. The fluids pressurize an actuator in a single operation or are discharged into the tubing or wellbore annulus through an exit port or valve. 
     Certain tools such as safety valves require fluid flow control in opposite directions. However, safety valves do not internally provide dual barrier capabilities because such barriers would resist two-way fluid flow. Because safety valves do not provide a passive well control barrier, significant design effort has been made to enhance the reliability of safety valve operation. Safety valves have been designed with metal-to-metal fittings, metal dynamic seals, rod piston actuators, and other features designed to provide reliable operation during a catastrophic event in the wellbore. Other safety valves use springs, annulus fluid pressure, or tubing fluid pressure to provide the restoring force necessary to return the closure mechanism to the original position. 
     Downhole well tool actuators generally comprise short term or long term devices. Short term devices include one shot tools and tools having limited operating cycles. Hydraulically operated systems have mechanical mechanisms with simple shear pins or complex mechanisms performing over multiple cycles. Actuation signals are provided through mechanical, direct pressure, pressure pulsing, electromagnetic, and other mechanisms. The control mechanism may involve simple mechanics, fluid logic controls, timers, or electronics. Motive force can be provided through springs, differential pressure, hydrostatic pressure, or locally generated mechanisms. Long term devices provide virtually unlimited operating cycles and are designed for operation through the well producing life. One long term device provides a fail safe operating capabilities which closes with spring powered force when the hydraulic line pressure is lost. Combination electrical and hydraulic powered systems have been developed for downhole use. 
     Control for a downhole tool can be provided by connecting a single hydraulic line to a tool such as an internal control valve (“ICV”) or a lubricator valve, and by discharging hydraulic fluid from the line end into the wellbore. This technique has several limitations as the hydraulic fluid exits the wellbore because of differential pressures between the hydraulic line and the wellbore. The discharge of hydraulic fluid into the wellbore comprises an undesirable environmental discharge, and the fluid discharge risks backflow and particulate contamination in the hydraulic system. Additionally, the setting depths are limited by the maximum pressure that a pressure relief valve can hold between the differential pressure between the control line pressure and the production tubing. All of these limitations effectively restrict single line hydraulic systems to relatively low differential pressure applications such as lubricator valves and sliding sleeves. 
     To overcome these limitations, a second hydraulic line can be installed to return hydraulic fluid to the wellbore surface through a closed loop. In U.S. Pat. No. 4,942,926 to Lessi (1990), dual hydraulic lines provided tool operation in two directions. In U.S. Pat. No. 3,906,726 to Jameson (1975), a manual control disable valve and a manual choke control valve controlled hydraulic fluid flow on either side of a piston head. In U.S. Pat. No. 4,197,879 to Young (1980) and in U.S. Pat. No. 4,368,871 to Young (1983), two hydraulic lines controlled a lubricator valve during well test operations. In all of these tools, two hydraulic lines are inefficient because the additional hydraulic lines increase sealing problems and reduce the available space through packers and wellheads. Additionally, passive barrier protection for each hydraulic line is not possible because of the return fluid flow from the well tool to the surface. 
     Accordingly, a need exists for an improved system capable of providing back pressure control in systems having multiple hydraulic lines. The system should be reliable, adaptable to different tool configurations and combinations, and should provide passive back flow containment for downhole well tools. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for providing back pressure control in at least two hydraulic lines extending downhole in a wellbore. The apparatus comprises a check valve engaged with each of the hydraulic lines in a closed initial position, wherein each of said check valves prevents pressurized fluid downhole of the check valves from moving upstream of the check valves, and hydraulic means operable with the fluid pressure in a hydraulic line to selectively open a check valve engaged with another of the hydraulic lines to permit two-way fluid communication through the check valve. The hydraulic means is further operable when the hydraulic line fluid pressure is reduced to return the check valve to the initial position. 
     In other embodiments of the invention, each check valve can comprise a pilot operated check valve, and the invention is applicable to three or more hydraulic lines. The hydraulic means can comprise a control valve or control valve combination having fewer valves than hydraulic lines. 
     In another embodiment of the invention, the apparatus can selectively open fluid flow through hydraulic lines extending between a wellbore surface and a downhole tool. The apparatus can comprise a check valve engaged with each hydraulic line in a closed initial position where each of the check valves prevents pressurized fluid downhole of the check valve from moving upstream of said check valve, a hydraulic means operable with the fluid pressure in a hydraulic line to selectively open a check valve engaged with another hydraulic line to permit two-way fluid communication through the check valve, and a controller engaged with the hydraulic lines for selectively pressurizing at least one of the hydraulic lines to operate said hydraulic means and to open a check valve engaged with another of the hydraulic lines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates engagement of a check valve in a hydraulic line. 
     FIG. 2 illustrates two hydraulic lines engaged having a pilot opening feature. 
     FIG. 3 shows a three-way three-position valve. 
     FIG. 4 illustrates a three hydraulic line application of the invention, wherein a valve is associate with each check valve. 
     FIG. 5 illustrates a four hydraulic line application of the invention. 
     FIG. 6 illustrates another application of the invention to a three hydraulic line system. 
     FIG. 7 illustrates another application of the invention to a four hydraulic line system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides passive back pressure control in multiple hydraulic lines, and is adaptable to systems having two or more hydraulic lines. The invention facilitates the creation of hydraulic line systems providing control functions and power requirements for the actuation of downhole well tools. 
     FIG. 1 illustrates the placement of conventional back check valve  14  in hydraulic fluid line  16 . Hydraulic line  16  can extend from the wellbore surface to engagement located downhole in the wellbore. As illustrated, the direction of fluid flow can move in one direction and is prevented from flowing in the opposite direction. FIG. 2 illustrates the application of the invention to two hydraulic fluid lines  18  and  20 , wherein pilot operated check valves  22  and  24  are integrated in fluid lines  18  and  20 . Check valves  22  and  24  operate as conventional check valves to prevent fluid flow upwards from the lower end of fluid lines  18  and  20 . However, pilot operated check valves  22  and  24  perform a different function when combined with another fluid pressure source. When fluid line  18  is pressurized, fluid moves downwardly through check valve  22  and is further directed through line  26  to check valve  24  to open check valve  24  to two-way fluid flow. Similarly, the separate operation of fluid line  20  moves fluid downwardly through check valve  24  and is further directed through line  28  to open check valve  22  to provide two-way fluid flow. When the fluid pressure within line  18  is removed, the pilot function for valve  24  is removed and valve  24  closes to provide a passive pressure barrier. When the fluid pressure within line  20  is removed, the pilot function for valve  22  is removed and valve  22  closes to provide a passive pressure barrier. 
     The extension of the invention to more than two hydraulic lines is accomplished by incorporating a valve for providing control over the pressure communication or flow of fluid from multiple lines. One such valve is illustrated in FIG. 3, wherein three-way, three-position piloted valve  29  has two positions and three ports. Two ports comprise inlet ports and the third comprises an outlet port. An internal, free floating check ball senses flow and pressure from the two inlet ports and closes the lessor flow inlet port in favor of the greater flow inlet port. In this manner, shuttle valve  29  automatically provides a switching function between multiple lines without requiring electrically operated solenoid valves, additional hydraulic lines, electronic controls, or other combinations conventionally used. Different combinations of pilot activated check valves and hydraulic switching valves such as shuttle valve  29  can be connected in series or in parallel in various configurations and combinations to accomplish different operating functions. This combination provides unique flexibility in providing back pressure control in complex hydraulic operating systems. 
     FIG. 4 illustrates a three hydraulic line system wherein pilot check valves  30 ,  32  and  34  are integrated with hydraulic lines  36 ,  38  and  40  to provide passive back pressure control. Non-selective valves  42 ,  44  and  46  are integrated into the system to selectively provide the pilot function for check valves  30 ,  32  and  34 . Pressurization of line  36  opens check valve  30  and further operates valve  44  to open check valve  32 , and operates valve  46  to open check valve  34 . Release of the pressure for line  36  causes check valves  30 ,  32  and  34  to close lines  36 ,  38  and  40 . Similarly, pressurization of line  38  opens check valve  32 , operates valve  42  to open check valve  30 , and further operates valve  46  to open check valve  34 . Release of the pressure for line  38  causes check valves  30 ,  32  and  34  to close lines  36 ,  38  and  40 . Pressurization of line  40  accomplishes a similar function of opening lines  36 ,  38  and  40 . The dual pressurization of two lines such as lines  36  and  38  opens check valves  30  and  32  and operates valve  46  to open check valve  34  because pressure from line  36  or line  38  will move through valve  46  to open check valve  34 . 
     FIG. 5 illustrates another embodiment of the invention applied to a four line system having lines  48 ,  50 ,  52  and  54 , check valves  56 ,  58 ,  60  and  62 , and valves  64 ,  66 ,  68 ,  70 ,  72 ,  74  and  76 . Pressurization of line  48  opens check valve  56 , operates valve  66  to operate valve  72  to open check valve  58 , operates valve  68  to operate valve  74  to open check valve  60  and to operate valve  76  to open check valve  62 . In this fashion, the pressurization of line  48  opens all four check valves  56 ,  58 ,  60  and  62 . Similarly, the pressurization of line  52  opens check valve  60 , operates valve  64  to operate valve  70  to open check valve  56 , operates valve  66  to operate valve  72  to open check valve  58 , and operates valve  76  to open check valve  62 . Withdrawal of pressure in line  52  causes each check valve to return to the initial closed position. 
     FIG. 6 illustrates another combination of components for a three line isolation system to selectively open and close lines  36 ,  38  and  40  with check valves  30 ,  32  and  34 . Valves  78  and  80  provide the functional operation provided by the three valves identified in FIG.  4 . Valves  78  and  80  provide a package for simultaneously opening check valves  30 ,  32  and  34 . When line  36  or line  38  is pressurized, such hydraulic fluid line pressure operates valve  78  to operate valve  80  to open the check valves. When line  40  is pressurized, valve  80  is operated to open the check valves. 
     FIG. 7 illustrates another embodiment of a four line isolation system to selectively open and close lines  48 ,  50 ,  52  and  54  with check valves  56 ,  58 ,  60  and  62 . Valves  82 ,  84 , and  86  provide the functional operation provided by the seven similar valves shown in FIG.  5 . When line  48  or line  50  is pressurized, such line pressure operates valve  82  to operate valve  84  and to operate valve  86  to open check valves  56 ,  58 ,  60  and  62 . When line  52  is pressurized, valve  84  operates valve  86  to open the check valves. When line  54  is pressurized, valve  86  is operated to open the check valves. 
     The invention is particularly suited to systems requiring hydraulic fluid reliability to the control of downhole well tools by uniquely utilizing hydraulics with logic circuitry. Such logic circuitry is analogous to electrical and electronics systems, and can incorporate Boolean Logic using “AND” and “OR” gate combinations. 
     The invention is particularly suitable for use with digital-hydraulic control systems serving multiple well control devices. In such system, pressure is applied in a coded sequence to several hydraulic lines. The coded sequence automatically selects one of the well control devices and provides independent operation of the well control device. Instead of discharging hydraulic fluid into the tubing or wellbore, excess fluid is returned up one of the unpressurized hydraulic lines. To permit return flow of the excess fluid, a system must permit such return flow through one or more hydraulic lines, and this return flow is provided by controlling the opening of the pilot operated check valves. 
     The invention provides passive back check valves on each hydraulic line. If one or more of the lines are pressurized from the wellbore surface, the back check valves in the unpressurized lines are temporarily opened with pilot pistons activated by the pressurized lines. In this configuration, the passive barriers provided by the back check valves are temporarily opened for two-way fluid communication to permit single tool operation or to permit selected tool operation for different combinations. After the pressure in a hydraulic line is removed and the line pressure is bled down or otherwise reduced, the back check valve on such hydraulic line closes to prevent fluid flow in such direction. Passive back pressure control is maintained because pressure from below does not open the back check valve, and the piloting pressure to open the back check valves is only provided by hydraulic line pressure above the valve. 
     Although the invention has been described in terms of certain preferred embodiments, it will become apparent to those of ordinary skill in the art that modifications and improvements can be made to the inventive concepts herein without departing from the scope of the invention. The embodiments shown herein are merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention.