Patent Application
20080237993
Subsurface safety valves SSVs are safety devices mounted deep within wells to control flow to the surface. They generally have many components in common. The valve member is generally a flapper, which rotates 90° and is held open by a flow tube shiftable downwardly therethrough to cause the 90° rotation. This direction of movement (opening) is away from a closure or seat. A control system is generally employed to urge the flow tube in the opening direction involving hydraulic pressure from the surface connected to the SSV below via a hydraulic control line. In general, applied pressure opens the valve, while removal of applied pressure from the surface allows a power spring acting on the flow tube to move the flow tube in a direction opposite the opening direction and thereby out of the path of the flapper. This allows the flapper to pivot 90° to a closed position.
Various types of control systems have been employed for SSVs in order to address various different issues or interests of an operator. To reduce the size of the closure spring acting on the flow tube, reservoirs pressurized with a gas have been used to counteract the hydrostatic pressure from the column of hydraulic fluid in the control line that runs from the surface down to the SSV. Since the pressurized gas resists the hydrostatic force and offsets it, closure of the SSV is accomplished with a fairly small spring when the actuating piston, acting on the flow tube, is placed in hydraulic pressure balance, thus allowing the small closure spring to shift the flow tube and allow the flapper of the SSV to close.
Such systems include pressurized reservoirs having a gas on one side and hydraulic fluid (liquid) acting on the opposite side of an actuating piston. In order to make such systems work, numerous seals are used. Control systems have also been developed that serve to allow normal opening and closing of the SSV while, at the same time, restricting the valve to fail in a predesignated safe position in the event of an occurrence of any of a number of different possible conditions or events relating to component failures in the control system. U.S. Pat. No. 6,109,351 (hereinafter “'351” and which is incorporated herein by reference in its entirety), for example, describes such a control system.
With the large number of seals in such a system and the requirement that many of the seals must maintain a seal while statically engaging with a piston and slidably engaging with a cylinder bore; seals are a major source of such component failure. Though the failsafe control system prevents undesirable uphole flow when a seal failure does occur it remains a costly undertaking to withdraw the SSV from downhole to repair and/or replace the defective seal or seals and run the SSV downhole again. As such, the art will welcome seals that exhibit improved durability and reliability.
Disclosed herein is a biased actuator. The actuator includes, a reservoir, at least one piston in operable communication with the reservoir, at least one metal seal disposed about the at least one piston and in substantial sealing communication therewith, the at least one metal seal further being in substantial sealing communication with the reservoir and a biasing system in operable communication with both the reservoir and the at least one piston.
Further disclosed herein is a control arrangement for a downhole valve. The control arrangement includes, at least one valve actuating piston having at least one metal seal sealingly engaging a housing in which the at least one valve actuating piston is movable, the at least one valve actuating piston having an opening force and a closing force, the opening force is connectable to a selectively controllable pressure source, a primary biasing arrangement acting on the closing force and a secondary biasing arrangement in selective operable communication with the closing force.
The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
A detailed description of an embodiment of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
The control system disclosed in '351 has two pistons and two gas charged reservoirs or chambers. One of the pistons is an actuating piston and the other is a balancing piston. Both pistons may be made of metal. The actuating piston moves a flow tube in a downhole direction in response to a pressure increase supplied from surface via a control line. The flow tube is moved in an uphole direction in response to urging from a power spring when the pressure in the control line is reduced below a predetermined value. The other piston is a pressure-balancing piston that isolates a primary gas charged pressure from the control line when all seals are properly sealing. The pressure-balancing piston allows the pressure of the primary gas charge to bleed to the control line and thereby equalize with the control line pressure in response to leakage of any of a plurality of control system seals. Each of the pistons in the control system has at least one seal that sealably engages with the piston and slidably sealably engages with cylinders in which the pistons are axially moveable. Disclosed herein is an exemplary embodiment of a subsurface safety valve with metallic seals employing the control system of '351.
Referring to
Through the foregoing structure the movement of the flow tube 18 between the uphole position and the downhole position facilitates the operation of the safety valve 10 between an open and closed position. As such, by controlling the position of the flow tube 18 the opening and closing of the safety valve 10 can be controlled.
Referring to
The seals 60, 62, 64 divide the cylinder 54 into four cavities 70, 72, 74, and 76. The seal 60 isolates the cavity 70 from the cavity 72, the seal 62 isolates the cavity 72 from the cavity 74, and the seal 64 isolates the cavity 74 from the cavity 76. The cavity 74 is fluidically connected, via a port not shown, to a downhole environment within which the safety valve 10 is located. Similarly, the cavity 70 is fluidically connected to a control line through a port not shown that ports control pressure from the surface to the safety valve 10. A longitudinal port 80 within each of the actuating pistons 42 fluidically connects the cavities 72 and 76 such that the cavities 72 and 76 are maintained at equal pressures at all times. Additionally, the cavity 76 is ported to a primary charge pressure via a portion of the control arrangement 14 that will be described with reference to
Referring to
The seals 90, 92 divide the cylindrical ports 104, 108 into three cavities 120, 122, and 124. The seal 90 isolates the cavity 120 from the cavity 122, and the seal 92 isolates the cavity 122 from the cavity 124 when the seal 92 is in sealing engagement with the first portion 112. The cavity 122 is fluidically connected through porting not shown to the control line, which is also fluidically connected to cavity 70 of
The foregoing structure is in accord with the failsafe control system of '351. As such failure of any of the seals 60, 62, 64, 90, and 92 will result in a pressure differential across the pressure-equalizing piston 84 so that it moves the seal 92 from sealing engagement with the first portion 112 to non-sealing engagement with the second portion 114. At this point the higher pressure of the pressurized gas charged primary reservoir (the cavities 124 and 76) is able to bleed to the control line (the cavities 122 and 70) thereby equalizing pressure between the pressurized gas charged primary reservoir and the control line. After which, the cavities 124, 76, 122 and 70 all have the same pressure therein. Once the pressure in cavities 124, 76, 122 and 70 is equalized the urging force of the power spring 26, which is set high enough to overcome the frictional and gravitational forces acting against it, is able to move the flow tube 18 to its uphole, or failsafe position, allowing the flapper 22 to close thereby preventing undesirable uphole fluid flow. Additionally, with the pressure-equalizing piston 84 no longer isolating the (control line) cavity 122, 70 from the cavity 124, 76, any increase in pressure in the control line will equalize about the actuating piston 42 preventing subsequent actuations of the safety valve 10 with increases in pressure in the control line. It should be that while the embodiment disclosed herein uses gas charged chambers to create biasing forces on the pistons 42, 84, alternate embodiments could create biasing forces using other sources of stored energy than chambers filled with a gas charge.
Referring to
The tubular member 128, therefore, is in the energized position when the portions 140, 144 are constrained within an assembly. In the energized position the portion 140 is sealably engagable with an inside sealing surface 148 of the housing 58, the fill block 96 or the housing 100, depending upon which seal 60, 62, 64, 90, and 92 is being used. A sealing force between the portion 140 and the inside sealing surface 148 is due to the energizing force of the tubular member 128 being in the energized position. This energizing force results from the elasticity of the metal from which the tubular member 128 is fabricated. Similarly, in the energized position the tubular member 128 has the portion 144 sealably engaged with an outside sealing surface 152 of the actuating piston 42 or the pressure-equalizing piston 84. A sealing force between the portion 144 and the outside sealing surface 152 is due to the energizing force of the tubular member 128 being in the energized position. This energizing force results from the elasticity of the metal from which the tubular member 128 is fabricated.
The elasticity of the metal tubular member 128 is such that the seal created between the tubular member 128 and the sealing surface 148, 152 is flexible enough to allow for minor movements of the pistons 42, 84 relative to the housings 58, 96, 100 without resulting in leakage therebetween. Additionally, the pistons 42, 84 and the tubular members 128 are axially slidably movable within the housings 58, 96, 100 while maintaining sealing engagement therebetween. The metal of the tubular member 128 can be highly resistant to degradation with long term exposure to high temperatures and high pressures that are commonly found in downhole environments. The metal of the tubular member 128 can also be highly resistant to corrosion and caustic fluids that may be encountered downhole as well. As such the sliding seal created between the seals 60, 62, 64, 90, and 92 and the housings 58, 96, 100, can have a high level of reliability and durability in very challenging applications.
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.
