Multi-pressure, single line supply system

A system for conveying fluid from a single subsea supply conduit to provide a fluid supply for each of a plurality of subsea well control apparatus requiring fluid supplies at different pressure levels. A fluid receiver receives fluid under pressure from the single subsea supply conduit, and a regulator regulates fluid flow from the receiver to charge one or more accumulators with fluid at desired pressure levels and to control injection of the fluid through an injection line into a subsea well flowline. The fluid used with the system may be glycol, methanol, or other suitable freezing retardants.

BACKGROUND OF THE INVENTION 
The field of this invention is fluid supply systems and the like. 
Offshore wells typically require a plurality of subsea well control devices 
which are remotely operated using fluid supplied from the ocean surface. 
Three basic functions performed by these control devices are control of 
gate valves, control of downhole safety valves, and injection of freezing 
retardant fluids into the flowlines coming from the wellhead. When flow 
valves in the wellhead are first opened and gas is released, gas in the 
flowline expands and may cause freezing. The injection of freezing 
retardant fluids such as methanol or glycol into the flowlines eliminates 
or reduces such freezing. 
Typically, the devices which perform the three control functions mentioned 
above each require an operating fluid supplied at a different pressure 
level. For example, the control device for controlling gate valves may 
require operating fluid at a pressure of 1500 to 300 p.s.i., and the 
device for controlling downhole safety valves may require operating fluid 
at pressures on the order of 6000 p.s.i. while fluid is injected to the 
flowlines at relatively high and variable pressures typically in the range 
from 2000 p.s.i. to 4700 p.s.i. 
Because of the differing fluid pressure requirements for the various 
control devices, operating fluid was often supplied through separate lines 
to each different control apparatus. Providing three or more flowlines for 
individually supplying operating fluid to the respective control devices 
was, of course, exceedingly expensive and somewhat unreliable. Other known 
systems employed booster arrangements and pumping arrangements to elevate 
the pressure of the operating fluid to the various desired levels. 
However, the addition of these active pumping means added not only expense 
but also inherent unreliability to such systems. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a new and improved supply 
system. 
The supply system of the present invention conveys fluid from a single 
subsea supply conduit to provide a fluid supply for each of a plurality of 
well control devices. The supply system is particularly adapted for use 
with well control devices, two or more of which have different supply 
pressure level requirements, and with a single subsea supply conduit which 
provides fluid alternately at such different pressure levels. 
A first embodiment of the supply system of the present invention includes a 
fluid receiving means for receiving the fluid from the single subsea 
supply conduit and at least two accumulators, each of which is mounted in 
a separate line and operably connected to a separate well valve control 
device. Each of the accumulators is, however, maintained in interruptible 
fluid communication with the fluid receiving means. A charging means 
operably connected to the fluid receiving means and to each of the 
accumulators charges the accumulators independently of one another with 
fluid from the fluid receiving means. Because the accumulators are in 
interruptible fluid communication with the fluid receiving means and are 
charged independently of one another, the accumulators may be separately 
charged to different pressure levels as the single subsea supply conduit 
provides fluid to the fluid receiving means at such different pressure 
levels. 
A second embodiment of the supply system of the present invention also 
includes a fluid receiving means for receiving fluid from the single 
subsea supply conduit. An injection means is in interruptible fluid 
communication with the fluid receiving means and controllably injects 
fluid from the fluid receiving means into a subsea well flowline. In 
addition, one or more accumulators are provided for supplying fluid to a 
subsea well valve control apparatus. The accumulator is mounted in a line 
separate from the injection means and is in interruptible fluid 
communication with the fluid receiving means for being charged with fluid 
from the fluid receiving means. A regulating means is operably connected 
to the fluid receiving means, the injection means, and the accumulator for 
regulating fluid flow from the fluid receiving means to control injection 
by the injection means and to control charging of the accumulator. The 
fluid used in the system is a freezing retardant fluid such as glycol or 
methanol, and this fluid serves as both the fluid for charging the 
accumulator and the fluid injected into the subsea well flowline by the 
injection means. One or more additional accumulators mounted in separate 
lines and connected to different control apparatus may also be placed in 
interruptible fluid communication with the fluid receiving means so that a 
plurality of accumulators may be charged independently of one another by 
the regulating means. The regulating means permits the accumulators to be 
charged to different pressure levels and fluid to be injected into a well 
flowline at a desired pressure level when the single subsea conduit 
provides fluid to the fluid receiving means at appropriate pressure 
levels. 
With both embodiments of the supply system of the present invention, fluid 
is conveyed from a single subsea supply conduit to provide a fluid supply 
for each of a plurality of well control devices, even where the well 
control devices require fluid supplies at different pressure levels. The 
elimination of multiple subsea supply conduits significantly reduces the 
cost of remotely operating the subsea well control devices and provides 
additional reliability to the system. Additionally, the embodiments of the 
present invention eliminate the inherent unreliability of systems 
employing boosters, alternate pumps, and other active pumping means 
because no such additional pumping means is required with the system of 
the present invention. Further, the second embodiment of the present 
invention permits the use of a single freezing retardant fluid as both the 
operating fluid for well control valve apparatus and the fluid to be 
injected into a well flowline by the injection means. In this manner, 
separate flowlines carrying different injection and operating fluids are 
eliminated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawings, the letter S designates generally the system of the 
present invention for conveying fluid from a single subsea supply conduit 
C to provide a fluid supply to two or more of a plurality of subsea 
control apparatus D, D', and D". The system S includes a fluid receiving 
means R which receives fluid under pressure from the single subsea supply 
conduit C. In a first embodiment of the present invention (FIG. 1), a 
charging means B charges two or more accumulator means A and A' 
independently of one another with fluid from the receiving means R, and, 
once charged, the accumulator means A and A' supply fluid to their 
associated control devices D and D'. In a second embodiment of the present 
invention (FIG. 2), one of the control devices D" is an injection means I 
for injection fluid from the fluid receiving means into a subsea well 
flowline. In this second embodiment, a regulator means M is provided to 
control charging of accumulator means A and A' with fluid from the fluid 
receiving means R and to control fluid injection by the injection means I. 
The system S of the present invention is particularly adapted for use on or 
near a subsea wellhead. The subsea supply conduit C extends to the system 
S from a remote location, typically the ocean surface. At the remote 
location, the conduit C is attached to a source of pressurized fluid, and 
the conduit conveys this pressurized fluid from the source to the 
receiving means R of the system S. The receiving means R is any suitable, 
commercially available flowline, coupling, connection, or the like which 
may be suitably joined with the conduit C to form a fluid tight seal and 
which provides a fluid passageway for fluid communication between the 
system S and the single subsea supply conduit C. 
In the first embodiment of the present invention, the receiving means R is 
in interruptible fluid communication with a first accumulator A through a 
flowline 12, a first accumulator valve 14, and a flowline 16. The first 
accumulator valve 14 is movable by means of an actuator 18 between an open 
position and a closed position. In its open position, valve 14 permits 
fluid flow between flowlines 12 and 16 so that fluid from the single 
subsea supply conduit C flows through the fluid receiving means R, 
flowline 12, valve 14, and flowline 16 to charge accumulator A with fluid 
from the single subsea supply conduit C. With valve 14 in its closed 
position, fluid flow between flowlines 12 and 16 is blocked by the valve 
so that the first accumulator A is isolated from flowline 12, receiving 
means R, and the single subsea supply conduit C. 
Similarly, a second accumulator A' is also in interruptible fluid 
communication with the receiving means R. A flowline 22, second 
accumulator valve 24, and a flowline 26 collectively provide an 
interruptible flow passageway from the receiving means R to the 
accumulator A'. The second accumulator valve 24 is movable between an open 
position and a closed position by an actuator 28. In its open position, 
the second accumulator valve 24 permits fluid flow between flowlines 22 
and 26 so that fluid under pressure from the single subsea supply conduit 
C flows through the fluid receiving means R, line 22, valve 24, and line 
26 to charge the accumulator A' with fluid from the single subsea supply 
conduit C. In its closed position, the second accumulator valve 24 blocks 
fluid flow between lines 22 and 26 so that the accumulator A' is isolated 
from line 22 and the fluid receiving means R. 
When charged with fluid from the single subsea conduit C through the 
receiving means R, each of the accumulators A and A' supplies a subsea 
well control apparatus with operating or control fluid. In a preferred 
embodiment of the present invention, each of the accumulators supplies 
fluid to a separate control apparatus. As shown in FIG. 1, the second 
accumulator A' supplies fluid through a flowline 30 to D'. The control 
apparatus D' as shown is a two position valve 34 operated by an actuator 
36 which controls operating fluid conveyed to in-line safety valves (not 
shown) or the like by a flowline 38. Valve 34 is opened and closed by 
actuator 36 upon receipt of an appropriate control signal to alternately 
allow fluid flow between lines 30 and 38 or block fluid flow between those 
lines. Once the accumulator A' has been charged with fluid from the supply 
conduit C and the fluid receiving means R, the second accumulator valve 24 
is closed so that the fluid from the accumulator A' flows only in the 
direction of the control apparatus D'. When the control valve 34 is 
opened, fluid flows from accumulator A' through line 30, valve 34, and 
line 38 to supply operating fluid to the in-line control valves. 
Accordingly, accumulator A' provides a source of operating fluid to the 
control apparatus D'. 
Similarly, accumulator A provides a source of operating fluid through a 
flowline 44 to control apparatus D which is a part of an electro-hydraulic 
control pod 40. Preferably, the electro-hydraulic control pod 40 is a 
conventional, commercially available ten function pod familiar to those 
having skill in the art. The control pod 40 has insulated electrical 
conductors 46 extending from it to a control panel located on the ocean 
surface. Control signals are transmitted to the electro-hydraulic control 
pod 40 by means of the conductor 46 to regulate hydraulic control signals 
and electrical control signals emitted from the control pod 40. 
The control pod 40 serves both as well control apparatus D which supplies 
control signals to various well control valve assemblies and as a portion 
of the charging means B. A first hydraulic signal line 42 extends from the 
control pod 40 and may be operably attached to wellhead control valves 
such as the gate valves on a subsea christmas tree. In response to an 
appropriate electrical signal provided through conductor 46, the flow of 
the control pod operating fluid through the hydraulic signal line 42 is 
controlled so that the gate valves are opened and closed as desired. 
Additionally, the electro-hydraulic control pod 40 may be provided with a 
second hydraulic signal flowline 48 which extends to the actuator 36 of 
the control apparatus D'. In response to an appropriate control signal 
transmitted to pod 40 by conductor 46, the flow of operating fluid from 
the control pod 40 to the actuator 36 is regulated so that the actuator 36 
opens and closes control valve 34 as desired to obtain the proper 
functioning of the in-line control valves operably attached to line 38. 
As previously mentioned, the electro-hydraulic control pod 40 additionally 
serves as a portion of the charging means B for the system S. The charging 
means additionally includes the first accumulator valve 14, the second 
accumulator valve 24, and the actuators 18 and 28 associated with 
respective accumulator valves. The control pod 40 is provided with a 
hydraulic control line 50 which extends to the actuator 28 for opening and 
closing the second accumulator valve 24. In response to an appropriate 
electrical signal conveyed to pod 40 by conductor 46, operating fluid of 
the pod 40 is passed through the hydraulic signal line 50 to control the 
operation of actuator 28 and thereby control the opening and closing of 
valve 24. Additionally, the electro-hydraulic control pod 40 is provided 
with an insulated conductor 52 which extends from the control pod 40 to 
actuator 18. In response to an appropriate electrical control signal 
provided to pod 40 through conductor 46, an electrical control signal is 
transmitted from the pod 40 through conductor 52 to control the operation 
of actuator 18 and thereby control the opening and closing of the first 
accumulator valve 14. 
The charging means B controls the fluid flow in the system S so that the 
first and second accumulators A and A' are charged independently of one 
another with fluid from the receiving means R. To charge the accumulators 
initially, a control signal is transmitted to the electro-hydraulic 
control pod 40 by conductor 46 which causes another electrical control 
signal to be transmitted through by conductor 52 to the actuator 18. In 
response to this latter control signal, the actuator 18 moves the first 
accumulator valve 14 to its open position so that fluid supplied through 
the single subsea conduit C flows through the receiving means R, flowline 
12, valve 14, and flowline 16 to charge the first accumulator A. Once the 
charging of the first accumulator A is complete, another control signal is 
conveyed from the pod 40 to actuator 18 by means of conductor 52 to cause 
the actuator 18 to close the first accumulator valve 14. The accumulator A 
is thus isolated from the flowline 12 and fluid receiving means R, and the 
accumulator A supplies operating fluid to the control pod 40 through 
flowline 44. Since the control pod 40 has a source of operating fluid once 
the accumulator A has been charged, the control pod is then used to 
hydraulically control the charging of the second accumulator A'. An 
electrical control signal is supplied to the pod 40 through conductor 46 
to cause a hydraulic fluid signal to be conveyed through flowline 50 to 
actuator 28. Upon receipt of the control signal the actuator 28 opens the 
second accumulator valve 24 and thereby permits fluid to flow from the 
subsea supply conduit C, through the fluid receiving means R, flowline 22, 
valve 24, and flowline 26 to charge the accumulator A' with fluid from the 
supply conduit C. Once the accumulator A' has been charged, another 
control signal is conveyed to the pod 40 by conductor 46, and the 
hydraulic signal through line 50 is removed to cause actuator 28 to close 
the second accumulator valve 24. Once the valve 24 is closed, the 
accumulator A' is isolated from flowline 22 and the fluid receiving means 
R and accumulator A' serves as a fluid supply for the control apparatus 
D'. Thus, it can be seen that the charging means B charges the first 
accumulator A and the second accumulator A' independently of one another 
with fluid from the fluid receiving means R. 
Since the accumulators A and A' are in separate lines and are isolated from 
one another after either valve 14 or valve 24 is closed, the accumulators 
A and A' may be charged to different pressure levels. With the single 
subsea supply conduit C operably connected to a source of pressurized 
fluid which alternately provides fluid at desired, different pressure 
levels, the opening and closing of the accumulator valves 14 and 24 may be 
regulated so that the respective accumulators A and A' are charged with 
fluid at different pressure levels. When the single subsea supply conduit 
C conveys fluid to the fluid receiving means R at a first pressure level, 
an electrical control signal is conveyed to pod 40 by conductor 46, and a 
control signal is passed over conductor 52 to actuator 18 which causes the 
valve 14 to open. With the valve 14 open, the first accumulator A receives 
fluid at a first pressure level from the fluid receiving means R and is 
thereby charged with fluid at that first pressure level. Another control 
signal is then conveyed to pod 40 through conductor 46, causing a control 
signal to be transmitted to actuator 18 over conductor 52 to close the 
first accumulator valve 14 and thereby isolate the first accumulator A 
from the fluid receiving means R. The source of pressurized fluid is then 
regulated to provide fluid through the supply conduit C at a second 
pressure level. A suitable control signal is next conveyed to control pod 
40 by conduit 46 to cause a hydraulic signal to be conveyed by line 50 to 
actuator 28, causing the actuator 28 to open the second accumulator valve 
24. The second accumulator A' is thus placed in fluid communication with 
the fluid receiving means R and is charged with fluid at the second 
pressure level. After the charging of the second accumulator A' has been 
completed, an additional control signal is conveyed to control pod 40 over 
conductor 46 to cause a different control signal to be transmitted to 
actuator 28 by flowline 50 and to close the second accumulator valve 24. 
Thus, both accumulators are isolated from one another and have been 
charged with fluid at different pressure levels to provide appropriate 
fluid supplies to their respective well control devices D and D'. 
The second embodiment of the present invention is schematically illustrated 
in FIG. 2. Many of the elements shown in FIG. 3 are substantially 
identical in structure and perform the same functions performed by 
corresponding elements previously described herein with reference to the 
first embodiment of the present invention. Accordingly, like letters and 
numerals are used in FIGS. 1 and 2 to designate like elements. 
The second embodiment of the present invention is a system for conveying 
fluid from the single subsea supply conduit C to provide a fluid supply 
for both subsea well valve control apparatus and fluid injection 
apparatus. The fluid receiving means R is in fluid communication with 
flowlines 58 and 60. The flowline 58 is operably connected to a first 
feeder conduit 62 so that a fluid passageway is provided between the fluid 
receiving means R and the first accumulator valve 14. Similarly, a second 
feeder conduit 64 is connected to the flowline 58 to place the fluid 
receiving means R in fluid communication with the second accumulator valve 
24. The flowline 60 maintains the fluid receiving means R in fluid 
communication with an injection valve 66 which is movable between open and 
closed positions by an actuator 68. With the valve 66 in its open 
position, the valve passes fluid between the flowline 60 and an injection 
line 70. With the valve 66 in its closed position, the valve blocks fluid 
flow between the flowline 60 and the injection line 70. 
The injection line 70 is a part of the fluid injection means I for 
injecting a fluid into a subsea well flowline 72. The injection line 70 
may be provided with a check valve 74 to ensure that fluid in line 70 
flows only from the injection valve 66 toward the well flowline 72. 
The injection line 70 is provided to convey a freezing retardant fluid into 
the well flowline 72 when the injection valve 66 is open. Once injected 
into the well flowline 72, the freezing retardant fluid retards or 
eliminates the freezing of fluids in the well flowline. With the second 
embodiment of the present invention, the subsea supply conduit C conveys 
such a freezing retardant fluid to the fluid receiving means R. 
Preferably, the freezing retardant fluid is glycol or methanol, but other 
suitable freezing retardant fluids may be utilized. 
With the second embodiment of the present invention, the freezing retardant 
fluid supplied by the single subsea supply conduit C through the fluid 
receiving means R not only serves as the injection fluid which is injected 
into the well flowline 72, but also serves as the fluid medium for 
charging both the first accumulator A and the second accumulator A'. In 
this manner, only one type of pressurized fluid needs to be supplied 
through the single subsea supply conduit C. Yet, a suitable source of 
fluid is provided by the system S for injecting fluid into the well 
flowline 72 and for providing fluid supplies for the subsea well valve 
control apparatus. 
With the second embodiment of the present invention, the regulating means M 
controls injection of fluid by the injection means I and controls the 
charging of the accumulators A and A'. The regulating means M includes a 
portion of control pod 40, accumulator valves 14 and 24, injection valve 
66, and the associated actuators 18, 28, and 68. The injection valve 66 
and the accumulator valves 14 and 24 are initially in their closed 
positions. An electrical control signal is supplied to the 
electro-hydraulic control pod 40 by conductor 46 to cause an electrical 
control signal to be conveyed by conductor 52 to the actuator 18 to open 
the first accumulator valve 14. With the first accumulator valve in its 
open position, fluid flows from the supply conduit C through the receiving 
means R, flowline 58, feeder conduit 62, valve 14, and line 16 to charge 
the first accumulator A with fluid. Subsequent to the charging of the 
first accumulator A, a second control signal is transmitted to the 
electro-hydraulic control pod 40 by conductor 46 to cause a different 
control signal to be transmitted to actuator 18 by conductor 52 so that 
the first accumulator valve 14 is closed. With the closing of the first 
accumulator valve 14 subsequent to the charging of the first accumulator 
A, the electro-hydraulic control pod 40 is provided with a source of 
operating fluid from the accumulator A through flowline 44. Another 
control signal is then conveyed to the control pod 40 by conductor 46 to 
cause a hydraulic pressure signal to be conveyed to actuator 28 through 
the actuator signal conduit 50. This signal causes the actuator 28 to open 
the second accumulator valve 24. With the second accumulator valve 24 is 
its open position, fluid flows from the subsea supply conduit C through 
the fluid receiving means R, flowline 58, feeder conduit 64, valve 24, and 
line 26 to charge the second accumulator A' with fluid from the single 
subsea supply conduit. Subsequent to the completion of the charging of the 
second accumulator A', another control signal is conveyed to the control 
pod by conductor 46, causing a different hydraulic control signal to be 
conveyed to actuator 28 through conduit 50. This latter hydraulic control 
signal causes the actuator 28 to close the second accumulator valve 24. At 
this point, both the first accumulator A and the second accumulator A' are 
charged with fluid and provide a fluid supply to the control pod 40 and 
the control apparatus D', respectively. The injection valve 66 may now be 
opened as desired to inject fluid from the single subsea supply conduit C 
into the well flowline 72 to prevent freezing in the latter flowline. A 
hydraulic signal conveying conduit 78 extends between the control pod 40 
and the actuator 68 to permit control of the opening and closing of the 
injection valve 66. Upon receipt of an appropriate control signal over 
conductor 46 by the control pod 40, a hydraulic pressure is exerted 
through the conduit 78 to the actuator 68 to cause the injection valve 66 
to open. With the valve 66 in its open position, fluid is conveyed from 
the single subsea supply conduit C, through the fluid receiving means R, 
flowline 60, injection valve 66, and injection line 70 into the well 
control flowline 72. Thus, with the second embodiment of the present 
invention, fluid is conveyed from the single subsea supply conduit C to 
provide a fluid supply for both the well valve control apparatus and the 
injection apparatus I. 
It will be appreciated, of course, that accumulators A and A' may be 
charged to different pressure levels and injection of fluid into well 
flowline 72 may be accomplished at yet a different pressure level. Where 
the single subsea supply conduit C is connected to pressurized fluid 
source which alternatively supplies fluid at three pressure levels, the 
opening and closing of valves 14, 24, and 66 may be regulated by 
appropriate signals to the control pod 40 to open the respective valves 
individually and at times when an appropriate pressure level is present in 
the fluid supply through the single supply conduit C. 
Preferably, each of the valves described herein have a failsafe closed 
construction. In this manner, leakage of fluid from either the system S or 
the control apparatus is reduced or eliminated in the event of a break in 
the associated flowlines or conduits. 
It should be understood, of course, that many variations of either of the 
two embodiments of the present invention described above are possible 
without departing from the spirit of the invention. For example, in the 
first embodiment of the present invention, additional accumulators could 
be connected to the fluid receiving means R to supply the same or other 
well control apparatus D. Similarly, in the second embodiment of the 
present invention, a single accumulator could be used with the fluid 
injection means I rather than having two accumulators as specifically 
illustrated in FIG. 3. 
However, with any of the embodiments of the present invention, fluid is 
supplied to a plurality of well control apparatus using only a single 
subsea supply conduit C. Additional supply conduits from the ocean surface 
are eliminated, thus substantially reducing the expenditures necessary 
when utilizing the system of the present invention. With each of the 
embodiments of the system S, multipressure supply levels are possible 
without having to utilize active pumping means which add to the inherent 
unreliability of known supply systems. 
The foregoing disclosure and description of the invention are illustrative 
and explanatory thereof, and various changes in the size, shape, and 
materials as well as in the details of the illustrated construction may be 
made without departing from the spirit of the invention.