Method for a 20 KSI BOP Stack with shared differential

Abstract

In a blowout preventer stack with two sealing elements which will not individually withstand the desired pressure differential the method of withstanding the desired pressure differential comprising providing a lower sealing element and an upper sealing element, providing a vent port in the bore below the lower sealing element to a relief valve, venting the outlet of the relief valve to the bore between the lower sealing element and the upper sealing element, adjusting the relief valve to limit the pressure allowed below the lower sealing element to a predetermined amount equal to or less than the working pressure of the lower sealing element.

Claims

1. In a blowout preventer stack with a bore and with two sealing elements which will not individually withstand the desired pressure differential, a method of withstanding the desired pressure differential comprising providing a lower sealing element and an upper sealing element, providing a vent port in the bore below the lower sealing element to a relief valve, venting the outlet of the relief valve to the bore between the lower sealing element and the upper sealing element, adjusting the relief valve to limit the pressure allowed below the lower sealing element to a predetermined amount equal to or less than the working pressure of the lower sealing element.

2. The method of claim 1, further comprising the upper sealing element and the lower sealing element are in the same blowout preventer body.

3. The method of claim 2, further comprising the upper sealing element and the lower sealing element are in the same blowout preventer body and the portion of the blowout preventer body housing the lower sealing element is of a higher working pressure than the portion of the blowout preventer body housing the upper sealing element.

4. The method of claim 1, further comprising the upper sealing element and the lower sealing element are in different blowout preventer bodies.

5. The method of claim 4, further comprising the upper sealing element and the lower sealing element are in separate blowout preventer bodies and blowout preventer body housing the lower sealing element is of a higher working pressure than the blowout preventer body housing the upper sealing element.

6. The method of claim 1, further comprising the relief valve is remotely controllable.

7. The method of claim 1, further comprising the sealing elements are the sealing element of an annular blowout preventer.

8. The method of claim 1, further comprising the sealing elements are the rams of a ram style blowout preventer.

9. The method of claim 1, further comprising one of the sealing elements is the sealing element of an annular blowout preventer and one of the sealing elements is the sealing element of an annular blowout preventer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a view of a contemporary deep-water riser system.

[0018] FIG. 2 is a perspective view of a blowout preventer stack utilizing the features of this invention.

[0019] FIG. 3 is a perspective view of a subsea wellhead housing which the blowout preventer stack of this invention would land on.

[0020] FIG. 4 is a perspective view of the lower portion of the blowout preventer stack of FIG. 2, generally called the lower BOP stack.

[0021] 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.

[0022] FIG. 6 is a perspective view of a section of the drilling riser which will be used to lower the blowout preventer stack.

[0023] FIG. 7 is a view of the blowout preventer stack of FIG. 2, taken along lines “7-7.

[0024] FIG. 8 is a view of the blowout preventer stack of FIG. 2, taken along lines “8-8.

[0025] FIG. 9 is a top view of FIG. 8.

[0026] FIG. 10 is cross section view of a double blowout preventer.

DETAILED DESCRIPTION OF THE INVENTION

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Referring now to FIG. 8, is a view of seafloor drilling system 100 taken along lines “8-8” of FIG. 1.

[0036] Referring now to FIG. 9, is a top view of seafloor drilling system 100.

[0037] Referring now to FIG. 10, blowout preventer 200 is shown having a lower thick-walled body section 202 capable of withstanding 20,000 p.s.i., an upper thinner walled body section 204 capable of handling 10,000 p.s.i., a central bore 206, a lower sealing element 208, and upper sealing element 210, a port 212 from the central bore below the lower ram 208 to a relief valve 214 set to a 10,000 p.s.i. pressure differential, and a port 216 to the central bore 218 between the lower sealing element 208 and the upper sealing element 210. When both the lower sealing element 208 and the upper sealing element 210 are closed, any pressure up to 10,000 p.s.i. will be sealed by the lower sealing element 208 and the upper sealing element 210 will not see any pressure differential. As the pressure differential exceeds 10,000 p.s.i., the relief valve 214 will begin to relieve the excess pressure and the upper sealing element 210 will seal all excess pressures above the 10,000 p.s.i. The sealing elements can be of a variety of types, with the most likely being such as the annular sealing elements shown in U.S. Pat. No. 3,572,627.

[0038] As 10,000 p.s.i. differential across the lower sealing element 208 puts very high stresses in the resilient materials, it may be preferable to distribute the pressure differential differently that a full 10,000 p.s.i. across the lower sealing element before beginning to load the upper sealing element. Relief valve 214 can be remotely controlled as is illustrated by line 220 going to controller 222 in a different pattern such as the differential being evenly divided between the sealing elements such that at a 10,000 p.s.i. total differential each of the sealing elements withstand is the stress of a 5,000 p.s.i. differential.

[0039] 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.