Safety valve utilizing an isolation valve

Abstract: A safety valve (100) for use in a well bore having an annulus. The valve (100) comprises a tubular valve housing having a valve closure member (132) captured therein and movable between an open and a closed position. An axially shiftable opening prong (130) is also captured in said housing for opening the valve closure member (132). A control line (104) is provided for supplying a hydraulic pressure to move the opening prong (130) against the closure member (132). A balance line (106) coupled to said tubular housing, and an isolation valve (108) coupled to said balance line (106).

Description: The present invention relates a subsurface safety valve and, more particularly, to a subsurface safety valve having a tubular housing and an axially shiftable flow tube used to manipulate a valve closure member. Subsurface safety valves (SSSVs) are used within well bores to prevent the uncontrolled escape of well bore fluids, which if not controlled could directly lead to a catastrophic well blowout. Certain styles of safety valves are called flapper type valves because the valve closure member is in the form of a circular disc or in the form of a curved disc. These flappers can be opened by the application of hydraulic pressure to a piston and cylinder assembly to move an opening prong against the flapper. The opening prong is biased by a helical spring in a direction to allow the flapper to close in the event that hydraulic fluid pressure is reduced or lost. Figures 1 and 2 illustrate a standard safety valve configuration 10 wherein a safety valve 14 is interposed in a tubing string 12. A control line 16 is used to open the valve. The valve 14 includes a tubular valve housing 28 with an axial passage 20. When hydraulic pressure is applied through port 22, the pressure forces a piston 24 to engage an axially shiftable opening prong 30. As the pressure forces the piston downward, the opening prong engages the closure member 32 and pushes the member into an open position. A spring 28 opposes the motion of the piston so that when the hydraulic pressure is released, the piston and opening prong are returned to a first position. The weight of the hydraulic fluid produces a "head" force against the piston, and thus is a factor in sizing the spring 28. In general, the pressure required to close the valve 14 is given by: Pressure closing = Force spring /Area piston Setting subsurface safety valves deeper is typically just a matter of ensuring sufficient closing pressure to offset the hydrostatic pressure acting to cause the valve to stay open. Increasing closing pressure is accomplished by increasing the Force spring or decreasing Area piston terms. As the valve closing pressure increases, so does the valve opening pressure. The surface capacity to provide operating pressure is a combination of the pressure needed to open the valve and the internal well pressure: Pressure surface = Pressure opening + Pressure well However, the available surface operating pressure can be limited by the umbilical line used to deliver the hydraulic pressure. It is not uncommon for that limit to be approximately 10,000 psi (68.9 MPa). Thus, if the surface pressure is fixed and the well pressure increases with depth, the opening pressure decreases with depth. For this reason, designs which operate independent of well pressure are required. Two well known designs are the dome charges safety valves and balance lines safety valves. A balance line valve 40 having a piston 48 in a housing 42 is illustrated in Figure 3. Two hydraulic chambers are pressurized on opposite sides of the piston 48. A control line is coupled to a first port 44 while the balance line is coupled to a second port 46. Each hydraulic line is filled with the same type of fluid. Hydrostatic pressure above and below the piston is equal. Thus, there is no downward force on the spring as a result of the hydrostatic pressure. The valve is operated by pressurizing the upper chamber. This increases the downward force, displacing fluid from the lower chamber and compressing the spring 50 to open the valve. Well pressure only has access to the seal diameters with cross-sectional areas A and A'. Well pressure acts upwards on A' and downwards on A. A and A' are equal, therefore well pressure has no upward or downward force on the piston as long as the seals at A and A' remain intact. Control line pressure acts downward on B-A while balance line pressure acts upward on B-A'. Thus, the hydrostatic pressures on opposite sides of the piston 48 are equalized. If seal 52 fails, well pressure enters the balance pressure chamber, acting on B-A, and increasing F3. If the well pressure is great, it may be impossible to supply sufficient surface pressure to the control line to force the opening prong downward. Thus, the safety valve fails to a closed position. If seal 54 fails, well pressure would enter the control chamber and act on B-A', increasing F3. Without applying control line pressure, the F1 would be greater than F2 + F3. This imbalance causes the valve to fail in an open position. The valve can be closed by pressuring up the balance line so that F3 + F2 is greater that the well assisted F1. This is only possible if sufficient balance line pressure can be applied. Another failure mode occurs when gas in the well fluid migrates into the balance line, reducing the hydrostatic pressure applied by the balance line, i.e., reducing F3. Another style of balance line safety valve is illustrated in Figure 4. The valve 60 has a piston 64 captured within a housing 62 and three hydraulic chambers 68, 70, and 72, two above and one below the valve piston. Two control lines are run to the surface. Well pressure acts on seals 74, 80. Since the piston areas A and A' are the same, well pressure has no influence on the pressure required to displace the piston. Control line and balance line hydrostatic pressures act on identical piston areas B-A' and B-A", so there is no net upward or downward force. If seal 74 leaks, well pressure accesses the balance line system. This pressure acts on area B-A", boosting force F3, which with F2 will overcome F1, to close the valve. If seal 76 leaks, communication between the control and balance lines will be established. F1 will always equal F3. Thus, F2 will be the only active force causing the valve to close. If seal 78 leaks, it has the same effect as seal 76 leaking. If seal 80 leaks, tubing pressure accesses the balance line system. This pressure acts to increase F3, overcoming F1 and closing the valve. Thus, if sufficient control line pressure is available and tubing pressure is relatively low, it may be possible to open the valve if seals 72 and/or 80 leak. Control line force F1 is greater than the tubing assisted balance force F3 with the spring force F2. In all modes of failure for this valve, the valve fails to a closed position. A dome charge safety valve uses a captured gas charge. The gas charge provides a heavy spring force to achieve an increased closing pressure. However, dome charge designs are complex and require specialized manufacturing and personnel. This increases the cost and decreases the reliability of the design because numerous seals are required. Also, industry standards favor metal-to-metal (MTM) sealing systems. Gas charges require the use of elastomeric seals. A need exists for a safety valve suitable for subsea applications and which is well pressure insensitive. Thus, it should incorporate the benefits of a balance line SSSV while overcoming the difficulties associated with gas migration into the balance line. Such a valve should also utilize MTM sealing systems for increased reliability. Finally, the improved valve should allow for the application of hydraulic pressure to close the valve in the event of a valve failure in an open position. US 4,621,695 discloses a well safety valve controlling flow through a well tubing using a hydraulic control line extending from the well surface to the one side of an actuating piston and cylinder assembly for opening the valve. A balance line extends to the second side of the piston and cylinder assembly for compensating for the hydrostatic pressure in the control line. The present invention relates to an improved safety valve that can be used in deep set applications by utilizing a simple pressure isolated chamber in combination with an isolation valve. The isolation could be part of the valve or a separate item. The isolation valve addresses the concerns typically associated with balance line concepts while also eliminating the need to contain a gas charge with elastomeric seals. The isolation valve is a key element of the solution. The isolation valve provides for volume exchange within the pressure isolated chamber during opening and closing. This further ensures that the necessary volume is provided even if some fluid exchange occurs between the first set of well isolation seals. The isolation valve also provides for pressure shut-off of the secondary line, while also preventing gas migration into the secondary line. It further provides for transfer of pressure from secondary line for closing valve for remedial cycling of the safety valve. The isolation valve also allows for the use of conventional SSSV technology whereas seal failure of the pressure isolation chamber does not impact the valve reliability after well pressure depletes. It is a lower cost solution with higher reliability. In combination with the secondary pressure line, the isolation seal differential is minimized by applying secondary line pressure. Finally, this design solution provides for common equipment between conventional completions and subsea completions. According to one aspect of the invention there is provided a safety valve for use in a well bore having an annulus, said valve comprising: (a) a tubular valve housing; (b) a valve closure member captured in said housing and movable between an open and a closed position; (c) an axially shiftable opening prong captured in said housing for opening the valve closure member; (d) a control line for supplying a hydraulic pressure to move the opening prong against the closure member; (e) a balance line coupled to said tubular housing; and (f) an isolation valve coupled to said balance line, characterised in that the isolation valve isolates said balance line from a gas migration from said safety valve. Advantageously, the isolation valve comprises a variable volume. In an embodiment, the safety valve further comprises a piston downwardly responsive to said hydraulic pressure from said control line, wherein said piston is displaceable into an annular chamber, and wherein said piston is coupled to the opening prong. In an embodiment, the safety valve further comprises a piston upwardly responsive to a hydraulic pressure from said balance line. In an embodiment, the balance line is coupled to a surface pressure source or to the annulus. The annular chamber may be in fluid communication with said isolation valve. The isolation valve may comprise a valve member which allows the one way passage of fluid. The isolation valve may isolate the balance line from a migration of gas into the balance line. According to another aspect of the invention there is provided a method of operating a safety valve placed in the flow path of a string of well tubing within a well annulus, said safety valve having a control line supplying a hydraulic pressure to an axially shiftable opening prong, said method comprising the steps of: (a) supplying a second source of hydraulic pressure through a second hydraulic line to an annular chamber within said safety valve, wherein said second source substantially balances a head pressure from said control line; and (b) isolating said second hydraulic line with an isolation valve. Advantageously, step (b) comprises providing an expandable volume to receive fluid displaced from within said safety valve. Step (b) may comprise isolating said second hydraulic line from a gas migration into said second hydraulic line. The method may further comprise applying a closing pressure to said valve through said second hydraulic line. The second hydraulic line pressure may exceed said control line pressure. Step (a) may comprise coupling said second hydraulic line to a surface pressure source or to a well annulus. Reference is now made to the accompanying drawings, in which: Figures 1 and 2 schematically illustrate a prior art safety vale having a single control line; Figure 3 illustrates a balance line safety valve having a balance line; Figure 4 illustrates an improved prior art balance line safety valve; Figure 5 illustrates an embodiment of a safety valve according to the present invention, utilizing an isolation valve on the second control line; and Figures 6a and 6b are sectional views across the length of an embodiment of a safety valve according to the invention. A safety valve 100 embodying the present invention is illustrated in Figures 5, 6a, and 6b. The valve 100 is placed in the flow path of tubing 102. A control line 104 is coupled to a first input port 122. When hydraulic pressure is applied through port 122, the pressure forces a piston 124 to engage an axially shiftable opening prong 130. As the pressure forces the piston downward, the opening prong engages the closure member 132 and pushes the member into an open position. A spring 128 opposes the motion of the piston so that when the hydraulic pressure is released, the piston and opening prong are returned to a closed position 132a. The closure member is biased to a closed position by a torsional spring 134. The weight of the hydraulic fluid produces a "head" force against the piston. A second hydraulic line 106 can be coupled to a second port 112 which allows it to supply hydraulic pressure to an annular chamber 114. The pressure in the annular chamber 114 can be used to counteract the hydraulic head from the control line 104, thereby making it easier for the spring 128 to lift the opening prong 130 to close the valve. Further, if the piston 126 or the opening prong 130 were to mechanically jam due to debris or otherwise, a lifting force could be applied through the second line 106. The isolation valve 108 contains a variable volume chamber. When the piston 126 is displaced downward by pressure applied through the control line 104, a volume of fluid beneath the piston 126, in annular chamber 114, is necessarily displaced. The displaced volume can flow back into the second line 106 and into the isolation chamber which expands to accommodate the displaced volume. The isolation chamber can be a housing with a movable piston for one wall. As displaced fluid enters the isolation chamber, the piston wall will move in response. In the embodiment discussed above, a second hydraulic line is coupled, through an isolation valve to second port 112. In an alternative embodiment, the second line 106 is open at 110 to the well annulus. By pressuring the annulus, the same functionality is achieved as with a second hydraulic line. In an alternate embodiment, the second line is closed at 110. In this case, while additional closing pressure cannot be applied, the isolation valve will allow for volume control of the fluid displaced by the piston when pressure is applied through the control line. Although preferred embodiments of the present invention have been described in the foregoing description and illustrated in the accompanying drawings, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications

Claims: A safety valve (100) for use in a well bore having an annulus, said valve (100) comprising: (a) a tubular valve housing; (b) a valve closure member (132) captured in said housing and movable between an open and a closed position; (c) an axially shiftable opening prong (130) captured in said housing for opening the valve closure member (132); (d) a control line (104) for supplying a hydraulic pressure to move the opening prong (130) against the closure member (132); (e) a balance line (106) coupled to said tubular housing; and (f) an isolation valve (108) coupled to said balance line (106), characterised in that the isolation valve (108) isolates said balance line (106) from a gas migration from said safety valve (100). A safety valve (100) according to claim 1, wherein said isolation valve (108) comprises a variable volume. A safety valve (100) according to claim 1 or 2, further comprising a piston downwardly responsive to said hydraulic pressure from said control line (104), wherein said piston is displaceable into an annular chamber (114), and wherein said piston is coupled to the opening prong (130). A safety valve (100) according to claim 1, 2 or 3, further comprising a piston upwardly responsive to a hydraulic pressure from said balance line (106). A safety valve (100) according to any preceding claim, wherein said balance line (106) is coupled to a surface pressure source. A method of operating a safety valve (100) placed in the flow path of a string of well tubing (102) within a well annulus, said safety valve (100) having a control line (104) supplying a hydraulic pressure to an axially shiftable opening prong (130), said method comprising the steps of: (a) supplying a second source of hydraulic pressure through a second hydraulic line (106) to an annular chamber (114) within said safety valve (100), wherein said second source substantially balances a head pressure from said control line (104); characterised by (b) isolating said second hydraulic line (106) with an isolation valve (108). A method according to claim 6, wherein step (b) comprises providing an expandable volume to receive fluid displaced from within said safety valve (100). A method according to claim 6 or 7, wherein step (b) comprises isolating said second hydraulic line (106) from a gas migration into said second hydraulic line (106). A method according to Claim 6, 7 or 8, further comprising applying a closing pressure to said valve (100) through said second hydraulic line (106). A method according to claim 9, wherein said second hydraulic line pressure exceeds said control line pressure.

Inventors: CROW ROBERT W, LEBOEUF GERALD L, MEADERS MICHAEL W, VINZANT MICHAEL B, CROW, ROBERT W., LEBOEUF, GERALD L., MEADERS, MICHAEL W., VINZANT, MICHAEL B.
Applicants: HALLIBURTON ENERGY SERV INC, HALLIBURTON ENERGY SERVICES, INC.
Application year: 1998
Main classification: E21B34
IPC codes: E21B34