U.S. patent application number 12/587983 was filed with the patent office on 2011-04-21 for constant environment subsea control system.
Invention is credited to Benton F. Baugh.
Application Number | 20110088913 12/587983 |
Document ID | / |
Family ID | 43878416 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110088913 |
Kind Code |
A1 |
Baugh; Benton F. |
April 21, 2011 |
Constant environment subsea control system
Abstract
The method of providing a pressurized control fluid for the
operation of subsea equipment of providing an accumulator with
control fluid pressurized by compressed gas, supplying the control
fluid to a control valve for the purpose of operating a function,
receiving a return flow of the control fluid from the function to a
control valve, directing the return flow of the control fluid to a
low pressure chamber whose pressure is substantially unaffected by
the subsea environmental pressure, and maintaining the low pressure
level in the low pressure chamber.
Inventors: |
Baugh; Benton F.; (Houston,
TX) |
Family ID: |
43878416 |
Appl. No.: |
12/587983 |
Filed: |
October 16, 2009 |
Current U.S.
Class: |
166/374 |
Current CPC
Class: |
E21B 34/16 20130101;
E21B 33/0355 20130101 |
Class at
Publication: |
166/374 |
International
Class: |
E21B 34/10 20060101
E21B034/10 |
Claims
1. The method of providing a pressurized control fluid for the
operation of subsea equipment comprising: providing an accumulator
with control fluid pressurized by compressed gas, supplying said
control fluid to a control valve for the purpose of operating a
function, receiving a return flow of said control fluid from said
function, directing said return flow of said control fluid to a
chamber whose pressure is substantially unaffected by the subsea
environmental pressure.
2. The method of claim 1, further comprising pumping the fluids out
of said low pressure reservoir.
3. The method of claim 2, further comprising pumping said fluids
into the ocean water.
4. The method of claim 2, further comprising pumping said fluids
back to the surface.
5. The method of claim 4, further comprising that the hose which
returns said fluids back to the surface is the same hose which
brought said fluids down from the surface.
6. The method of claim 1, further comprising flooding said low
pressure reservoir with water to sweep any accumulated gas out of
said low pressure reservoir.
7. The method of claim 6, further comprising said water to sweep
said accumulate gas is control fluid from the surface.
8. The method of claim 6, further comprising said water to sweep
said accumulate gas is sea water.
9. The method of claim 8, further comprising said sea water to
sweep said accumulate gas is pumped by the same pump which will
pump fluids out of said reservoir.
10. The method of claim 8, further comprising said sea water to
sweep said accumulate gas is pumped by a different pump than the
pump which pumps fluids out of said reservoir.
11. The method of providing a pressurized control fluid for the
operation of subsea equipment comprising: providing an accumulator
with control fluid pressurized by compressed gas, supplying said
control fluid to a control valve for the purpose of operating a
function, receiving a return flow of said control fluid from said
function to a control valve, directing said return flow of said
control fluid to a chamber whose pressure is substantially
unaffected by the subsea environmental pressure.
12. The method of claim 11, further comprising pumping the fluids
out of said low pressure reservoir.
13. The method of claim 12, further comprising pumping said fluids
into the ocean water.
14. The method of claim 12, further comprising pumping said fluids
back to the surface.
15. The method of claim 14, further comprising that the hose which
returns said fluids back to the surface is the same hose which
brought said fluids down from the surface.
16. The method of claim 11, further comprising flooding said low
pressure reservoir with water to sweep any accumulated gas out of
said low pressure reservoir.
17. The method of claim 16, further comprising said water to sweep
said accumulate gas is control fluid from the surface.
18. The method of claim 16, further comprising said water to sweep
said accumulate gas is sea water.
19. The method of claim 18, further comprising said sea water to
sweep said accumulate gas is pumped by the same pump which will
pump fluids out of said reservoir.
20. The method of claim 18, further comprising said sea water to
sweep said accumulate gas is pumped by a different pump than the
pump which pumps fluids out of said reservoir.
Description
TECHNICAL FIELD
[0001] This invention relates to the general subject of providing a
pressurized working fluid for the operation of subsea equipment,
especially in very deep waters.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] Not applicable
REFERENCE TO A "MICROFICHE APPENDIX"
[0004] Not applicable
BACKGROUND OF THE INVENTION
[0005] The field of this invention is that of deepwater control
systems for the purpose of providing a supply of pressurized
working fluid for the control and operation of equipment. The
equipment is typically blowout preventers (BOP) which are used to
shut off the well bore to secure an oil or gas well from accidental
discharges to the environment, gate valves for the control of flow
of oil or gas to the surface or to other subsea locations,
hydraulically actuated connectors and similar devices. The fluid to
be pressurized is typically an oil based product or a water based
product with added lubricity and corrosion protection.
[0006] The working fluid for such control systems typically comes
from accumulators. Currently accumulators have historically come in
three styles which operate on a common principle. The principle is
to precharge them with pressurized gas to a pressure at or slightly
below the anticipated minimum pressure required to operate
equipment. Fluid can be added to the accumulator, increasing the
pressure of the pressurized gas and the fluid. The fluid introduced
into the accumulator is therefore stored at a pressure at least as
high as the precharge pressure and is available for doing hydraulic
work.
[0007] The accumulator styles are bladder type having a balloon
type bladder to separate the gas from the fluid, the piston type
having a piston sliding up and down a seal bore to separate the
fluid from the gas, and a float type with a float providing a
partial separation of the fluid from the gas and for closing a
valve when the float approaches the bottom to prevent the escape of
gas.
[0008] Accumulators providing typical 3000 p.s.i. working fluid to
surface equipment can be of a 5000 p.s.i. working pressure and
contain fluid which raises the precharge pressure from 3000 p.s.i.
to 5000 p.s.i.
[0009] As accumulators are used in deeper water, the efficiency of
conventional accumulators is decreased. In 1000 feet of seawater
the ambient pressure is approximately 465 p.s.i. For an accumulator
to provide a 3000 p.s.i. differential at 1000 ft. depth, it must
actually be precharged to 3000 p.s.i. plus 465 p.s.i. or 3465
p.s.i.
[0010] At slightly over 4000 ft. water depth, the ambient pressure
is almost 2000 p.s.i., so the precharge would be required to be
3000 p.s.i. plus 2000 p.s.i. or 5000 p.s.i. This would mean that
the precharge would equal the working pressure of the accumulator.
Any fluid introduced for storage would cause the pressure to exceed
the working pressure, so the accumulator would be
non-functional.
[0011] Another factor which makes the deepwater use of conventional
accumulators impractical is the fact that the ambient temperature
decreases to approximately 35 degrees F. If an accumulator is
precharged to 5000 p.s.i. at a surface temperature of 80 degrees
F., approximately 416 p.s.i. precharge will be lost simply because
the temperature was reduced to 35 degrees F. Additionally, the
rapid discharge of fluids from accumulators and the associated
rapid expansion of the pressurizing gas causes a natural cooling of
the gas. If an accumulator is quickly reduced in pressure from 5000
p.s.i. to 3000 p.s.i. without chance for heat to come into the
accumulator (adiabatic), the pressure would actually drop to 2012
p.s.i.
[0012] A more recent solution to this problem has been what is
referred to as constant differential accumulators as is illustrated
in U.S. Pat. No. 6,202,753. These accumulators use a double piston
looking like a barbell which acts as mechanical summing relay. On
the top side of the top piston is the gas charge similar to the
more conventional accumulators. On the lower side of the upper
piston is the pressurized working fluid. The lower piston is
connected to the upper piston by a connecting rod. Seawater
pressure is vented onto the top side of the lower piston, pushing
it down and therefore pulling the upper piston down harder onto the
working fluid. A vacuum is on the lower side of the lower piston
and so offers no support. The net effect is that the working fluid
pressure is generally equal to the sum of the nitrogen pressure
plus the seawater pressure. In other words its pressure is always
higher than the ambient pressure by the amount of the nitrogen
pressure. This provides a good solution irrespective of depths, but
provides a relatively costly construction.
[0013] Subsea drilling has been done for about 60 years and during
that time drilling has occurred in progressively deeper and deeper
water. The deeper water is associated with colder temperatures
making the deepwater use of accumulators especially difficult.
Substantial and ongoing research has been done to try to make
conventional accumulators operational in waters in depths of
greater than 6,000'. From there it only gets more difficult as
drilling is now happening in depths as great as 12,000'. This has
resulted in very high nitrogen precharges simply to be higher than
the pressure at these ocean depths along with concerns about
liquefying the nitrogen charge gas. As industry and standards
societies have pursued the difficulties of making conventional
accumulators work in conventional situations, a better solution is
needed.
[0014] The problem being discussed here is that the environment in
which the accumulators are working is changing. The different
pressure and temperature combinations of various have been a
problem for the industry for many years, and is only exaggerated as
the drilling depths continue to be deeper and deeper.
SUMMARY OF THE INVENTION
[0015] The object of this invention is to provide a control system
for deepwater ocean service which allows the equipment to be
operated as if it were in a constant environment.
[0016] A second object of this invention is to provide a control
system for deepwater ocean service which does not lose its
operating differential across subsea working pistons due to high
deep sea ambient pressures.
[0017] A third object of the present invention is to provide a
control system for deepwater ocean service which operates with
similar characteristics when deep sea and during surface
testing.
[0018] Another object of the present invention is to provide a
control system which operates in conjunction with conventional
accumulators rather than requiring constant differential
accumulators.
[0019] Another object of this invention is to provide a system
which does not require high gas precharge pressures so that they
will have a differential above ambient pressures at sea depths.
[0020] Another object of this invention is to provide a system
which does not present a concern with gas pressures high enough and
temperatures low enough to provide the possibility of liquefying
the compressed gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a partial section of a system of subsea equipment
utilizing the control system in the mode of pushing the blowout
preventer rams forward to seal across the bore.
[0022] FIG. 2 is a partial section of a system of subsea equipment
utilizing the control system in the mode of blocking the movement
of the blowout preventer ram.
[0023] FIG. 3 is a partial section of a system of subsea equipment
utilizing the control system in the mode of retracting the blowout
preventer rams from the bore
[0024] FIG. 4 is a partial section of a system of subsea equipment
utilizing the control system in the mode of emptying the low
pressure reservoir of control fluids.
[0025] FIG. 5 is a partial section of a system of subsea equipment
utilizing the control system in the mode of flooding the low
pressure reservoir with sea water to eliminate any accumulated
gas.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] Referring now to FIG. 1, a blowout preventer (BOP) stack 10
is landed on a subsea wellhead system 11, which is supported above
mudline 12. The BOP stack 10 is comprised of a wellhead connector
14 which is typically hydraulically locked to the subsea wellhead
system 11, multiple ram type blowout preventers 15 and 16, an
annular blowout preventer 17 and an upper mandrel 18. A riser
connector 19, and a riser 20 which extends to the surface are
attached for communicating drilling fluids to the surface.
[0027] Blowout preventer 16 includes a body 30, rams 32 and 34 for
moving into the vertical bore 36, connecting rods 38 and 40,
pistons 42 and 44, outer chamber 46 and 48, and inner chambers 50
and 52.
[0028] When lines 60 and 62 are pressured, the pistons 42 and 44,
connecting rods, 38 and 40, and rams 32 and 34 move toward the
centerline of the bore 36 to seal off the bore 36 when appropriate.
When lines 64 and 66 are pressured, the components are retracted
from bore 26.
[0029] Control valve 70 is a 3 position valve which is utilized to
operate the blowout preventer 16 and is illustrative of dozens of
valves which become part of a subsea control system. In the
position as shown the control valve 70 receives fluid along line 72
from accumulator 74 and delivers it along line 76 and in turn to
lines 60 and 62 to move the rams 32 and 34 towards the bore 36.
Accumulator 74 can be any of the conventional accumulators as
indicated in the background of the invention.
[0030] Conventionally, the return fluid coming out of line 64 and
66 through line 78 are vented to the subsea environment. At a
10,000 ft. depth, this subsea environment is at a
10,000.times.0.465 p.s.i./ft.=4650 p.s.i. This is extremely hard
work to do for a conventional accumulator, with the only workable
solution being the more expensive constant differential
accumulators as described in the background of this
application.
[0031] In this embodiment, the flow out of lines 64 and 66 goes
through line 78, through control valve 70, through line 80, through
check valve 82 and into reservoir 84. Reservoir 84 is simply an
empty bottle at or near atmospheric pressure which will withstand
the external pressures of the sea water. If the gas pressure in
accumulator 74 is 3000 p.s.i. and the pressure in reservoir 84 is
zero, the operating differential pressure across the pistons 42 and
44 is 3000 p.s.i., irrespective of depth. It operates exactly the
same at 10,000 ft. as it does at the surface.
[0032] Three position control valve 70 is shown with two opposing
electric actuators 90 and 92 along with centering springs 94 and
96. As actuated with electricity sent electric actuator 92, program
section 98 is active and delivers fluid from the accumulator 74 to
the outer chambers 46 and 48. As the pistons 42 and 44 move
forward, the fluid in inner chambers 50 and 52 is flushed out to
the reservoir 84.
[0033] Hydraulic line 104 directs a supply of hydraulic control
fluid from the surface through check valve 102 and into accumulator
74 to keep the accumulator 74 charged with pressurized control
fluid. Electric line 100 is illustrative of control wires coming
from the surface to do tasks such as operating control valve
70.
[0034] Referring now to FIG. 2, the electric signal has been
removed from the electric actuator 92 and the two springs 94 and 96
have centralized the valve on program section 106. In this case the
flow is blocked and the rams 32 and 34 will remain stationary in
their present position.
[0035] Referring now to FIG. 3, an electric signal is sent to
electric actuator 90 and has moved program section 110 to the
active position. In this position control fluid will be directed
from the accumulator 74, through line 78, through lines 64 and 66
to the inner chambers 50 and 52. This will push the pistons 42 and
44 away from the bore and thereby move the rams 32 and 34 away from
the bore.
[0036] Referring now to FIG. 4, when control fluid collects in
reservoir 84 during operations, electric motor 120 drives pump 122
and pumps the control fluids out of line 124 to the ocean as
indicated by arrow 126. The control fluids will be environmentally
friendly. Alternately, the fluid can be returned to a hose back to
the surface, such as hose 104.
[0037] Referring now to FIG. 5, if there is any gas entrained in
the control fluids, they will tend to accumulate as a gas in the
low pressure reservoir 84. Over time, a collection of gas in
reservoir 84 can impede the performance of the system. Higher gas
pressure in reservoir 84 reduces the pressure differential from
accumulator 74. If motor 120 and therefore pump 122 is reversed,
reservoir 84 will be completely filled with seawater up to flowing
out of check valve 132 as indicated by arrow 132. When reservoir 84
is completely filled with water, the entrained gas will be pushed
out check valve 130 also. At that time the motor 120 and pump 122
can be returned to the normal pumping direction and remove the
water from the reservoir 84, as is seen in FIG. 4. By this
procedure a low pressure gas or vacuum can be maintained in
reservoir 84.
[0038] 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.
* * * * *