Method for gate valve failsafe actuators
In a subsea blowout preventer stack system with valves in the choke and kill lines with the need for failsafe operation or automatic movement of a safe position when the operating control signal is lost, a method of providing failsafe operation to the safe position comprising providing a hydraulic cylinder having a piston with a piston rod connected to the valve closure member, providing a first hydraulic supply at a first pressure to a first side of the piston to move the valve closure member to an actuated position, providing a second hydraulic supply at a second pressure lower than the first pressure to a second side of the piston to move the valve closure member to the safe position when the first hydraulic supply is removed.
This invention relates to the method of providing failsafe gave valve actuators, especially at it applies to large gate valves and 20,000 p.s.i. blowout preventer stacks.
CROSS-REFERENCE TO RELATED APPLICATIONSNot applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable
REFERENCE TO A “MICROFICHE APPENDIX”Not applicable
BACKGROUND OF THE INVENTIONDeepwater offshore drilling requires that a vessel at the surface be connected through a drilling riser and a large blowout preventer stack to the seafloor wellhead. The seafloor wellhead is the structural anchor piece into the seabed and the basic support for the casing strings which are placed in the well bore as long tubular pressure vessels. During the process of drilling the well, the blowout preventer stack on the top of the subsea wellhead provides the second level of pressure control for the well. The first level being provided by the weighted drilling mud within the bore.
During the drilling process, weighted drilling mud circulates down a string of drill pipe to the drilling bit at the bottom of the hole and back up the annular area between the outside diameter of the drill pipe and the inside diameter of the drilled hole or the casing, depending on the depth.
Coming back up above the blowout preventer stack, the drilling mud will continue to travel back outside the drill pipe and inside the drilling riser, which is much large than the casing. The drilling riser has to be large enough to pass the casing strings run into the well, as well as the casing hangers which will suspend the casing strings. The bore in a contemporary riser will be at least twenty inches in diameter. It additionally has to be pressure competent to handle the pressure of the weighed mud, but does not have the same pressure requirement as the blowout preventer stack itself.
As wells are drilled into progressively deeper and deeper formations, the subsurface pressure and therefore the pressure which the blowout preventer stack must be able to withstand becomes greater and greater. This is the same for drilling on the surface of the land and subsea drilling on the surface of the seafloor. Early subsea blowout preventer stacks were of a 5,000 p.s.i. working pressure, and over time these evolved to 10,000 and 15,000 p.s.i. working pressure. As the working pressure of components becomes higher, the pressure holding components naturally become both heavier and taller. Additionally, in the higher pressure situations, redundant components have been added, again adding to the height. The 15,000 blowout preventer stacks have become in the range of 800,000 lbs. and 80 feet tall. This provides enormous complications on the ability to handle the equipment as well as the loadings on the seafloor wellhead. In addition to the direct weight load on the subsea wellheads, side angle loadings from the drilling riser when the surface vessel drifts off the well centerline are an enormous addition to the stresses on both the subsea wellhead and the seafloor formations.
When the blowout preventer stack working pressure is increased to 20,000 p.s.i. some estimates of the load is that it increases from 800,000 to 1,200,000 lbs. The height also increases, but how much is unclear at this time but it will likely approach 100 feet in height.
Another complication is that gate valves used in the choke and kill lines on these stacks must be rated at 20,000 p.s.i. also and must be automatically closed when there is a loss of the control signals. The high frictions caused by the high forces caused by potential 20,000 p.s.i. differentials are conventionally handled by large metal spring cartridges. The springs are extremely hard to design and obtain for these forces and in combination with the necessary housings they are installed in become not only very heavy but also relatively large. There are always at least six of these assemblies on the over weight crowded subsea blowout preventer stacks.
This has been the situation is subsea blowout preventer stacks since their early use in the 1960s and is more of a problem now than ever as the size and working pressure of this equipment both keep getting larger.
BRIEF SUMMARY OF THE INVENTIONThe object of this invention is reduce the weight, size, and cost of subsea blowout preventer stacks.
A second object of this invention is to provide a failsafe means for gate valves on subsea blowout preventer stacks which do not depend on large spring cartridges.
A third object of this invention is to make a valve which can be switched form failsafe closed to failsafe hose by simply changing the fitting connections.
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Blowout preventer stack 60 is landed on a subsea wellhead system 64 landed on the seafloor 66. The blowout preventer stack 60 includes pressurized accumulators 68, kill valves 70, choke valves 72, choke and kill lines 74, choke and kill connectors 76, choke and kill flex means 78, and control pods 80.
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In some cases it is beneficial to have the valve move to the failsafe opened position rather than the failsafe closed position. In the case of gate valves, this usually means making installing a special gate with the hole in the gate in a different position. In the case of this operator, the line attached to fitting 226 needs to be moved to the fitting 244 and the line 236 needs to be moved to the fitting 226.
This method will apply to gate valves, ball valve, plug valves and other type valves. The safe position is typically the closed position of a valve, but in some cases the operational safe position has been the open position.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
Claims
1. In a subsea blowout preventer stack system with valves in the choke and kill lines with the need for failsafe operation or automatic movement of a safe position when the operating control signal is lost,
- a method of providing failsafe operation to the safe position comprising
- providing a valve closure member,
- providing a hydraulic cylinder having a piston with a piston rod connected to the valve closure member,
- providing a first hydraulic supply at a first pressure to a first side of the piston to move the valve closure member to an actuated position,
- providing a second hydraulic supply at a second pressure lower than the first pressure to a second side of the piston to move the valve closure member to the safe position when the first hydraulic supply is removed,
2. The method of claim 1, providing the valve closure member is a gate.
3. (canceled)
4. (canceled)
5. The method of claim 1, providing the second hydraulic supply is from a constant different accumulator.
6. The method of claim 1, providing the failsafe position is the valve is closed.
7. The method of claim 1, providing the failsafe position is the valve is opened.
8. The method of claim 5, providing the first hydraulic supply is from a constant differential accumulator.
9. The method of claim 8, providing the first hydraulic supply pressure relative to ambient is approximately twice the second hydraulic supply pressure relative to ambient.
Type: Application
Filed: Jul 28, 2021
Publication Date: Feb 2, 2023
Inventor: Benton Frederick Baugh (Houston, TX)
Application Number: 17/386,824