Abstract
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.
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.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a view of a contemporary deep-water riser system.
[0016] FIG. 2 is a perspective view of a blowout preventer stack utilizing the features of this invention.
[0017] FIG. 3 is a perspective view of a subsea wellhead housing which the blowout preventer stack of this invention would land on.
[0018] FIG. 4 is a perspective view of the lower portion of the blowout preventer stack of FIG. 2, generally called the lower BOP stack.
[0019] FIG. 5 is a perspective view of the upper portion of the blowout preventer stack of FIG. 2, generally called the lower marine riser package or LMRP.
[0020] FIG. 6 is a perspective view of a section of the drilling riser which will be used to lower the blowout preventer stack.
[0021] FIG. 7 is a view of the blowout preventer stack of FIG. 2, taken along lines “7-7.
[0022] FIG. 8 is a view of the blowout preventer stack of FIG. 2, taken along lines “8-8.
[0023] FIG. 9 is a top view of FIG. 8.
[0024] FIG. 10 is view of a pair of block valves similar to item 128 in FIG. 4.
[0025] FIG. 11 is taken along lines “11-11” of FIG. 10 showing the body of a block valve.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Referring now to FIG. 1, a view of a system 20 which might use the present invention is shown. It shows a floating vessel 22 on a body of water 24 and having a derrick 26. Drill pipe 28, drilling mud system 30, control reel 32, and control cable 34 are shown. A riser system 40 including a flex joint 42 is shown. During drilling the drilling mud circulated from the drilling mud system 30, up the standpipe 44, down the drill pipe 28, through the drill bit 46, back up through the casing strings 48 and 50, through the blowout preventer stack 60, up thru the riser system 40, and out the bell nipple at 62 back into the mud system 30.
[0027] 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.
[0028] Referring now to FIG. 2, the seafloor drilling system 100 comprises a lower blowout preventer stack 102, a lower marine riser package 104, a drilling riser joint 106, and control cables 108.
[0029] Referring now to FIG. 3, a subsea wellhead is shown which the seafloor drilling system lands on. It is the unseen upper portion of the subsea wellhead system 64 shown in FIG. 1.
[0030] Referring now to FIG. 4, the lower blowout preventer stack 102 comprises a lower structural section 120, vertical support bottle 122, and upper structural section 124, accumulators 126, choke and kill valves 128, blowout preventers 130 and an upper mandrel 132 which will be the connection point for the lower marine riser package.
[0031] Referring now to FIG. 5 the lower marine riser package 104 is shown comprising a lower marine riser package structure 140, an interface 142 for a remotely controlled vehicle (ROV), annular blowout preventers 146, choke and kill flex loops 148, a flexible passageway 150, a riser connector 152, and an upper half of a riser connector 154.
[0032] Referring now to FIG. 6, a drilling riser joint 106 is shown having a lower half of a riser connector 160, a upper half of a riser connector 154, and buoyancy sections 162.
[0033] Referring now to FIG. 7, is a view of seafloor drilling system 100 taken along lines “7-7” of FIG. 1 showing wellhead connector 170, lower marine riser connector 172, a man 174 for size perspective, and choke and kill valves 176.
[0034] Referring now to FIG. 8, is a view of seafloor drilling system 100 taken along lines “8-8” of FIG. 1.
[0035] Referring now to FIG. 9, is a top view of seafloor drilling system 100.
[0036] Referring now to FIG. 10, block valves 200 and 202 are shown to be similar, except valve block 202 does not have a lower outlet. The block valves are connected directly together requiring that the flow from the lower block valve passes through the valve 204 of the upper block valve 200. As a practical matter, the valve 206 on lower block valve 202 can be eliminated and the lower valve block can depend upon valve 204 as the back up valve. The block valves 200 and 202 are attached to the blowout preventer stack by flanges 208 and 210 as can be seen as item 128 in FIG. 4. The valves are normally actuated by ports such as indicated at 212 which is distal from the valve body. The return side of the gate valve actuators are connected with lines 214 proximate to the valve body as will be described later.
[0037] Referring now to FIG. 11 which is taken along lines “11-11” of FIG. 10 showing the body 220 of a block valve, the gate 222 in the open position on one side of the centerline and in the closed position on the other side of the centerline, a clamp style bonnet connection 224, a fitting 226 for filling the operating cylinder 228 with actuating fluid, and a return chamber 230. On a conventional valve the return chamber 230 would be large and filled with mechanical springs to return to the closed or failsafe position if the control system failed. The failsafe position would be considered to be the safe position of the valve. As the forces on these valves with a 20,000 p.s.i. differential are great, it is very difficult to design springs to provide this service. Additionally, as the return chamber with springs changes volume when the valve is actuated, extra consideration must be taken to accommodate the fluid volume. The valve of this invention rather utilizes a constant differential accumulator just like the large ones on the blowout preventer stack providing the fluid for operating cylinder 228, only smaller and at half the pressure charge. If the main accumulators are working at 3000 p.s.i., the smaller accumulators 232 will be charged to approximately 1500 p.s.i. so that the 3000 p.s.i. will be able to overwhelm the 1500 p.s.i. on the return side to operate, but when the 3000 p.s.i. operating signal is dropped to zero, the 1500 p.s.i. will close the valves safely. Constant differential accumulators such as this are described U.S. Pat. No. 6,202,753. On accumulator 232, working fluid is stored in chamber 234 and is communicated to the return chamber 230 through line 236. Nitrogen gas charge pressure is in chamber 238. Compensating seawater pressure is introduced into chamber 240 and chamber 242 has a vacuum or simply standard air pressure in it.
[0038] 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.
[0039] 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.
[0040] 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.
