The present invention relates generally to devices for controlling fluid flow in a bore in a subterranean formation and, more particularly (although not necessarily exclusively), to devices that are capable of controllably preventing or allowing the production of fluid through a well traversing a subterranean formation using a flow tube that can move at least partially independent to a piston.
Production tubing can be positioned in a downhole environment of a wellbore in a fluid-producing formation. Fluid from the formation can travel through the production tubing to a surface of the wellbore. The production tubing can include a safety valve that is controllable by hydraulics, electrical signals, or another control mechanism. The safety valve may be a sub-surface safety valve. The safety valve can open to allow fluid to flow through the production tubing. The safety valve can close to prevent fluid from flowing through the production tubing.
For example, in response to an accident, a control action at the surface, or otherwise a decrease of hydraulic fluid pressure, the safety valve can allow a flow tube that is part of the safety valve and the production tubing to move toward the surface, resulting in a flapper to close and seal the flow tube (and thus the production tubing) from fluid from the formation.
A closing flapper or other closing mechanism can exert force on the flow tube, which may result in damage to the flapper assembly, a pressure spike in a control line for the hydraulic fluid, and other undesirable results. For example, as the flapper is close to closing, the pressure differential across the flapper can force the flow tube toward the surface with a large amount of force. The large amount of force may break the flapper or seat hinge, shear a hinge pin, warp the flow tube, and impart momentum into the flow tube. In some situations, 1250 pound force (lbf) is transferred to the flow tube for every 100 psi of pressure differential across the flapper.
Safety valves are desirable that can handle forces from flappers or other closing mechanisms during closing.
Certain aspects and features of the present invention are directed to a safety valve that can include a flow tube that is allowed to move at least partially independent, or free, from a piston assembly to avoid negative effects from forces on the flow tube from a closing assembly.
One aspect relates to a safety valve that can be disposed in a wellbore through a fluid-producing formation. The safety valve includes a piston assembly, a flow tube, a closing assembly, and a connecting assembly. The piston assembly can be controlled from a surface of the wellbore. The closing assembly can allow and prevent fluid flow through an end of the flow tube. The connecting assembly can be positioned between the flow tube and the piston assembly. The connecting assembly can allow the flow tube to move toward the surface of the wellbore in response to a closing force exerted on the flow tube by the closing assembly and at least partially independent of movement toward the surface of the wellbore by at least part of the piston assembly.
Another aspect relates to a connecting assembly for a safety valve that can be disposed in a wellbore through a fluid-producing formation. The connecting assembly includes a first end, a second end, and a receiving member. The first end can couple to a piston assembly. The second end can engage a power spring that supports the flow tube. The receiving member can allow the flow tube to move toward the surface of the wellbore in response to a closing force exerted on the flow tube by a flapper and at least partially independent of movement toward the surface of the wellbore by at least part of the piston assembly.
Another aspect relates to a safety valve that can be disposed in a wellbore through a fluid-producing formation. The safety valve includes a piston rod, a flow tube, a normally-closed flapper, and a ring assembly. The piston rod can be controlled by a piston and by hydraulic fluid introduced into the wellbore from the surface. The normally-closed flapper can be positioned proximate to an end of the flow tube for allowing and preventing fluid flow through the end of the flow tube. The ring assembly can be positioned between the flow tube and the piston assembly and external to part of the flow tube. The ring assembly can allow the flow tube to move toward the surface of the wellbore in response to a closing force exerted on the flow tube by the normally-closed flapper and at least partially independent of movement toward the surface of the wellbore by the piston rod.
These illustrative aspects are mentioned not to limit or define the invention, but to provide examples to aid understanding of the inventive concepts disclosed. Other aspects, advantages, and features of the present invention will become apparent after review of the entire disclosure, figures, and claims.
Certain aspects and features of the present invention are directed to a safety valve that can be disposed in a wellbore that is through a fluid-producing formation. The safety valve can include a flow tube that is allowed to move at least partially independent, or free, from a piston assembly to avoid negative effects from forces on the flow tube from a closing assembly, such as one including a flapper. For example, the flow tube may not be required to be rigidly connected to a piston assembly and instead “floats” such that the flow tube can move more than the piston assembly moves.
A safety valve according to one example includes a connecting assembly between a flow tube and a piston assembly. The safety valve may be a sub-surface safety valve. The piston assembly may include a piston and a piston rod that are configured to move in response to the presence or absence of hydraulic fluid pressure, or in response to another control mechanism. A closing assembly may be located proximate to an end of the flow tube and be capable of closing and opening for controlling fluid flow to the flow tube. The end of the flow tube may be an opening into which fluid can flow, but is not necessarily an end of the production tubing, which may extend many feet into the wellbore past the flow tube. A closing assembly may include components such as a flapper valve, a ball valve, or a poppet valve. For example, a flapper valve can include a spring-loaded plate that can open to allow formation fluids to flow into the flow tube and that can close to prevent formation fluids from flowing into the flow tube.
The piston assembly can move away from the surface in response to an increase in hydraulic fluid pressure, or some other control mechanism, that may be introduced via a control line. The piston assembly moving away from the surface can exert a force on the connecting assembly to move correspondingly in a direction away from the surface. Moving correspondingly can include a component moving the same or similar distance as another component. The connecting assembly can exert a force on the flow tube (either directly or indirectly, such as through a power spring) to cause the flow tube to move correspondingly in a direction away from the surface. The flow tube moving away from the surface can cause the closing assembly to open and allow fluid to flow through the flow tube toward the surface.
Some event, such as controls from the surface or an emergency with respect to the well, may result in a reduction or absence of hydraulic fluid pressure. In response to the reduction or absence of hydraulic fluid pressure, the piston assembly may move toward the surface and the connecting assembly may move correspondingly toward the surface. The flow tube may also move correspondingly toward the surface. As the flow tube moves toward the surface, the closing assembly can begin to close an end of the flow tube. As the closing assembly begins to close, the closing assembly can exert a force on the flow tube in a direction toward the surface. For example, fluid may be flowing at 200 ft/s, resulting in a relatively large force on the closing assembly as it begins to close. The piston assembly, however, may not be capable of allowing the flow tube to move toward the surface faster to diminish or remove the forces exerted on the flow tube as the closing assembly is closing. For example, the piston assembly may move toward the surface relatively slowly. The connecting assembly can be configured to allow the flow tube to move at least partially independent of the piston assembly for some additional distance toward the surface to allow the closing assembly to close faster and diminish or reduce the forces exerted on the flow tube by the closing assembly during closing. As the piston assembly moves toward the surface more than the additional distance, the flow tube can resume moving correspondingly with respect to the piston assembly toward the surface.
In one example, the connecting assembly includes a ring disposed external to the flow tube and defining a chamber between an outer wall of the flow tube and an inner wall of the ring. The chamber can allow the flow tube to move toward the surface at least partially independent of movement by the piston assembly in response to a force from the closing assembly. In some aspects, the connecting assembly may include a take-up spring disposed in the chamber. The take-up spring can prevent the flow tube from moving toward the surface unintentionally, such as when the flow tube is in a position such as that the closing assembly is open, but can allow forces exerted on the flow tube during closing to overcome the biasing force of the take-up spring and allow the flow tube to move at least partially independent to the piston assembly. As the force exerted on the flow tube during closing diminishes, the take-up spring can bias the flow tube so that the flow tube can resume moving toward the surface correspondingly with the piston assembly.
A connecting assembly according to some aspects may allow a flow tube to move a half inch or more at least partially independent to movement by the piston assembly. For example, a connecting assembly may allow the flow tube to move up to 2-3 inches at least partially independent to movement by the piston assembly. In some implementations, the connecting assembly may allow the flow tube to move within a range of 1 to 6 or more inches at least partially independent to movement by the piston assembly.
Safety valves according to certain aspects may reduce forces on a pin or hinge of a closing assembly during slam closure, reduce forces on an upstop of the safety valve during slam closure, reduce damage between the closing assembly and an opening prong, and/or allow a closing assembly to close faster. A safety valve may reduce pressure spikes in a control line during slam closure, reducing forces that may cause damage to a control line fitting, piston, seals, and piston rod. For example, hydraulic fluid pressure in the control line during closing may be around 2000 psi. Forces exerted on the flow tube, and transferred to the hydraulic fluid, may increase the hydraulic fluid pressure to 34,000 psi. A safety valve according to some examples can reduce or eliminate such spiking in response to closing forces. Certain safety valves may provide a spring force on an upstop seat in the closed position, reduce stresses experienced by a flapper or seat hinge of the closing assembly, and/or align the spring force with the piston.
These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional features and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative features but, like the illustrative features, should not be used to limit the present invention.
A production tubing 112 extends from the surface within wellbore 102. The production tubing 112 can define a passageway providing a conduit for production of formation fluids to the surface.
The safety valve assembly 114 can be a subassembly of the production tubing 112. A control line 116 may be positioned between the safety valve assembly 114 and the surface. The control line 116 can be in communication with the safety valve assembly 114 for delivering controls, such as through hydraulic fluid pressure. The safety valve assembly 114 can open and close in response to the presence and absence of hydraulic fluid pressure to control fluid flow through the production tubing 112.
Although
The piston assembly 202 and control line port 212 may be in a top subassembly 214. The top subassembly 214 may be configured to couple the safety valve 114 to another part of the production tubing that is closer to the surface than the safety valve 114. The closing assembly 208 may be in a bottom subassembly 216. The bottom subassembly 216 may be configured to couple the safety valve 114 to another part of the production tubing that is farther from the surface that the safety valve 114. The connecting assembly 206 and power spring 210 may be in a spring housing 218.
The piston assembly 202 may include a piston (part of which is shown as 220) and a piston rod 222. Hydraulic fluid pressure can be received through port 212 to cause the piston to move away from or toward the surface of the wellbore. The moving piston can cause the piston rod 222 to move correspondingly. The piston rod 22 can coupled to the connecting assembly 206 and cause the connecting assembly 206 to move correspondingly.
The connecting assembly 206 can engage the power spring 210. For example, the connecting assembly 206 may be coupled, directly or indirectly, to the power spring 210 or physically configured to contact the power spring 210, to engage the power spring 210. The connecting assembly 206 can transfer force from the piston rod 222 to the power spring 210 to compress the power spring 210. The power spring 210 may be biased to allow the closing assembly 208 to be normally closed. For example, when hydraulic pressure is reduced at the piston, the power spring 210 can exert a force on the connecting assembly 206 and the piston rod 222 to move toward the surface. The power spring 210 in
The compressed power spring 210 can allow or cause the flow tube 204 to move away from the surface of the wellbore and open the closing assembly 208. Fluid can flow through the flow tube 204 when the closing assembly 208 is open.
The connecting assembly 206 includes a ring 224 and a take-up spring 228 that is disposed in a chamber 226 defined by the ring 224. The chamber 226 can be between an outer wall of the flow tube 204 and at least part of the inner wall of the ring 224. The take-up spring 228 may be biased to extend outward, such as away from the surface. The take-up spring 228 in
The chamber 226 can receive part of the flow tube 204 as the closing assembly 208 is closing. Force exerted on the flow tube 204 by the flapper 211 as in
For example and referring to
The flow tube 204 can move these additional 2 inches at least partially independent to movement of the piston. For example, the piston may move a small amount during this process, and the flow tube 204 can move an amount corresponding to this small amount, in addition to approximately 2 inches that the flow tube 204 is allowed to move. The flow tube 204 moving the additional 2 inches can allow the flapper 211 to close faster than otherwise and reduce the effects of the force of the flapper 211 on the flow tube 204 and other system components during closing. After the piston has moved toward the surface the additional 2 inches, following the example, the flow tube 204 can resume moving correspondingly, or substantially correspondingly, to the movement of the piston.
The flow tube 302 includes a first component 312 coupled to a second component 314. The first component 312 can rest against the top subassembly 306.
The connecting assembly 308 is similar to the previously described connecting assembly, except that the connecting assembly 308 can be round without reduced areas to provide different coupling provides with respect to the piston rod 304.
Two coupling mechanisms 316 couple the piston rod 304 to the connecting assembly 308. An example of a coupling mechanism is a nut, or a bolt and nut combination. Gaps 318 may be between the coupling mechanism 316 and the connecting assembly 308. The gaps 318 may be relatively small and may allow the piston rod 304 to move at least partially independent with respect to the connecting assembly 308. For example, when the flow tube 302 stops moving toward the surface, the first component 312 contacts the top subassembly 306 but the gaps 318 allow the piston (not shown) associated with the piston rod 304 to contact a piston upstop seat.
In other implementations, the coupling mechanisms 316 can be adjusted away from the surface, such as by one quarter inch such that the first component 312 is prevented from contacting the top subassembly 306, but the piston is allowed to be forced against the upstop by the power spring 310.
The foregoing description of the aspects and examples, including illustrated features, of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of this invention.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US12/44310 | 6/27/2012 | WO | 00 | 6/13/2013 |