System and Method to Improve Operation of Hydraulic Pump for Subsea Service

Abstract

The operating performance and reliability of a pump, e.g. a hydraulic pump, can be significantly improved by incorporating an actively controlled positive displacement control valve in fluid communication with a fixed displacement pump, supply fluid line, and return fluid line. In use, the pump may be used to move fluid from the suction side to the discharge side of the pump, including fully opening the suction circuit to the pump cylinder and fully closing the pump discharge circuit during a pump suction stroke, fully closing the suction circuit and fully opening the pump discharge circuit to a downstream circuit during a pump discharge stroke, and allowing fluid to be pumped without the fluid passing through a valve spring loaded check valve.

Description

CLAIM TO PRIORITY

This application claims the benefit of priority under 35 U.S.C. §119(e) from U.S. Provisional Patent Application No. 61/762,743 entitled “Method to Improve Operation of Hydraulic Pump for Subsea Service”, filed Feb. 8, 2013, which is incorporated herein in its entirety by this reference.

FIELD OF THE INVENTION

The operating performance and reliability of a pump, e.g. a hydraulic pump, can be significantly improved by incorporating “Positive Displacement Control Valve” technology as shown in the following figures and description.

BACKGROUND OF THE INVENTION

A single cycle of a reciprocating piston pump typically has two components: a suction stroke and a discharge stroke. During the pump suction stroke, fluid flows through a pump suction port into the pump cylinder. The movement of the pump piston usually draws the fluid from a local reservoir or supply conduit. With the pump discharge stroke, the fluid within the pump cylinder is pushed out of the pump by the pump piston; exiting through a pump discharge port where it is routed to a different location like, for example, a pipeline or tank.

In the simplest terms, a pump moves fluid from the suction side to the discharge side of the pump, and, in doing so, adds energy to the displaced fluid. As a secondary effect of moving the fluid through the pump, the pump generally reduces pressure on the suction side while increasing pressure on the discharge side of the pump.

A pump must be driven by a mechanism that supplies the energy to move the pump piston. A simple hydraulic driven intensifier pump is really two back-to-back hydraulic cylinders. One hydraulic cylinder contains a piston which is cyclically reciprocated by a separate hydraulic power unit and directional control valve. This “drive cylinder” is mechanically linked to, thereby also reciprocating, a second piston in a “pumping cylinder.”

Fluid must flow through the pump in only one direction; from the suction port to the discharge port. In conventional pumps, check valves are used in the suction and discharge lines to/from the pump to ensure that the flow is uni-directional. These check valves are, in general, spring loaded, poppet-and-seat type valves that only allow flow through the valve in one direction. A pressure differential in the “flow” direction moves the poppet off the seat, compressing the spring, and opening a flow path through the check valve. When this pressure differential sufficiently decreases, the spring forces the poppet against the seat, closing off the reverse flow path through the check valve. By automatically responding to internal pressure differentials, check valves provide automatic passive operation requiring no additional external controls. Check valves provide a simple and effective solution for controlling flow direction in conventional pumping applications. However, as will be explained below there are several disadvantages with using check valves in the unconventional applications as we have in deepwater subsea oilfield service.

Check valves are sensitive to solid contaminants in the fluid being pumped. The geometry of the poppet and seat arrangement in a check valve tends to trap contaminants between the poppet and seat preventing the check valve from shutting off flow in the reverse “no-flow” direction. This is a major limitation of check valves in any service involving contaminated liquids.

One growing unconventional subsea application requires the use of pumps to reduce the pressure in a subsea piping system that has been blocked due to a hydrocarbon “ice” (methane hydrate or methane clathrate) plug that can form under certain conditions. Reducing the pressure around the plug causes the ice to melt, allowing the piping circuit to be restored to normal operation. The lower the pressure that can be achieved by the pump, the faster the ice plug will melt.

Another application includes the use of subsea pumps for delivering various treating chemicals into the subsea well or production piping system. In most of these cases, the volume of chemical delivered must be controlled and measured. So the subsea pump becomes not only a fluid pumping device, but also a fluid volumetric metering device; hence the name “metering pump”. Metering pumps are commonly used for conventional non-subsea applications. Indeed, the conventional pump depicted in the original disclosure is commonly used for chemical metering applications for conventional non-subsea applications.

There are several limitations to using conventional pump check valves in certain applications. The oilfield piping circuit containing the ice plug can contain significant solid contaminants that can become lodged in the pump check valves resulting in pumping system failure. Plugs can sometimes be composed of hydrate mixed with other materials common in crude oil that can plug lines, like asphaltenes, waxes or polymer formations. The pressure in the piping circuit can only be reduced to the opening pressure of the pump suction check valve; increasing the time that it takes to melt the ice plug. The basic design of a reciprocating pump in gas service is limited by the “pressure ratio” which is an engineering relationship between pump stroke volume and operating pressure of the pump check valves. There is also a significant limitation to using conventional check valves in unconventional subsea pumping applications.

After some period of continued production from a subsea oilfield, the pressure in the hydrocarbon reservoir, and downstream piping system, decreases to a level below which the treating chemical will actually free-flow or “auto-siphon” from the storage reservoir through the pump check valves and into the subsea piping system bypassing the capability and purpose of the metering pump to control the volume of chemical used. Indeed the chemical metering pump discharge pressure in a subsea production system may vary from 15,000 psi to −4000 psi relative to the pump suction pressure over the production life of a deepwater oilfield.

One possible way of mitigating this auto-siphoning effect is to introduce an in-line relief valve or back-pressure valve downstream of the pump. However this type of device is subject to high mechanical stresses, sensitive to contamination, and must be adjusted for changing conditions over the field life.

FIGURES

The figures supplied herein disclose various embodiments of the claimed invention.

FIG. 1 is a block diagram of an exemplary embodiment of a pump; and

FIG. 2 is a block diagram of an exemplary embodiment of a system incorporating a pump.

DESCRIPTION OF VARIOUS EMBODIMENTS

Referring generally to FIG. 1 and FIG. 2, the operating performance and reliability of a subsea pump can be improved by incorporating the technology as shown in the following figures and description. In its embodiments, the disclosed system 1 (FIG. 2) may be technology used for, e.g., subsea chemical injection pumping systems and presents an improvement in subsea pumps used for hydrate remediation work.

As will be apparent to those of ordinary skill in subsea pump arts, in the various embodiments system 1 may be used to help prevent auto-siphoning of fluids through pump when operating in sub-ambient discharge conditions; provide positive displacement operation allowing metered flow of fluids independent of suction or discharge conditions; eliminate lower reliability spring-loaded check valves; provide full flow bores through pump suction and discharge to improve contamination resistance; allow lower suction pressure, which is an advantage to pipeline scavenging operations such as a subsea hydrate remediation operation; and provide a pump design that is not limited by compression ratio.

Referring to FIG. 1, in an embodiment, system 1 (FIG. 2) comprises subsea pump 2 useful for subsea service. Subsea pump 2 comprises fixed displacement pump 10, inlet valve 21 in fluid communication with fixed displacement pump 10; supply fluid line 25 in fluid communication with inlet valve 21; return fluid line 26 in fluid communication with inlet valve 21; outlet valve 23 in fluid communication with fixed displacement pump 10; suction line 32 in fluid communication with outlet valve 23; and discharge line 36 in fluid communication with outlet valve 23.

In preferred embodiments fixed displacement pump 10 comprises drive cylinder 11, further comprising drive piston 12 which is cyclically reciprocated by a separate hydraulic power unit and directional control valve (not shown in the figures) and pumping cylinder 13, further comprising pumping piston 14 which is cyclically reciprocated by the separate hydraulic power unit and directional control valve.

However, fixed displacement pump 10 may be driven hydraulically, electrically, and/or mechanically. Additionally, valves 20,30 may be controlled actively and/or passively and may further be operated hydraulically, electrically, and/or mechanically.

Drive cylinder 11 may be operatively linked to pumping cylinder 13. In some embodiments, drive cylinder 11 is larger than pumping cylinder 13.

Referring additionally to FIG. 2, system 1 may further comprise active controller 40 operatively connected to the fixed displacement pump 10 and valves 20,30. Active controller 40 may further comprise instrumentation 41 suitable for feedback, such as a position sensor, a pressure sensor, a temperature sensor, a flow meter, a sensor configured to aid in fluid qualitative analysis, or the like, or a combination thereof.

In certain embodiments, positive displacement control valve 30 may be configured using very robust, contamination resistant, hardened metal seal elements similar to those used in subsea oilfield gate valves and blowout preventer (BOP) control systems. This type of seal element is capable of shearing even large solid contaminants that may enter positive displacement control valve 30 when, for example, pumping liquids from a hydrocarbon pipeline.

In the operation of exemplary embodiments, operation of subsea pump 2 may be improved for a subsea service by using the disclosed system which can be used without requiring spring loaded check valves. In general, the method includes the use an actively controlled positive displacement control valve 30 in the pumping circuit instead of conventional check valves, as described above. In its embodiments, this method allows fluid to be pumped without passing through a check valve, eliminating many limitations of a pump that uses this type of valve. Subsea pump 2, which is more contamination resistant and inherently more reliable, is capable of reducing the suction pressure without the limitation of overcoming the spring force in the suction check valve. Additionally, the pump design is no longer as limited by compression ratio as prior art pumps.

Platform mounted chemical metering pumps are commonly used to inject chemicals into subsea wells and flowlines via long umbilical tubes extending to the subsea injection point. However, the deepwater subsea applications, largely in the Gulf of Mexico, have only recently matured to the point where the subsea production pressures are lower than the minimum possible controllable delivery pressure of a topsides metering pump. There is starting to be significant volumes of chemical being inadvertently injected into subsea wells and flowlines from these platforms, and this problem will increase in the coming years. Even in this topsides pump application, positive displacement control valve 30 would be an improvement over conventional technology.

Subsea services may comprise preventing auto-siphoning of the fluid through a chemical metering pump in applications where the discharge pressure is lower than the suction pressure. One advantage of the disclosed method is to prevent auto-siphoning of fluid through a chemical metering pump in applications where the discharge pressure is lower than the suction pressure. Additionally, subsea services may comprise using positive displacement control valve 30 where a pressure of a subsea production is lower than the minimum possible controllable delivery pressure of a topsides metering pump. Further, subsea services may include chemical injection into a fluid flowline, chemical metering, hydraulic fluid supply and power, pressure management, integrity testing, blockage remediation, or the like, or a combination thereof.

Subsea pump 2 is typically disposed subsea. As described herein, positive displacement control valve 30 is disposed in the pumping circuit and comprises two internal valve circuits 31,33 that act to alternately open and close the pump suction and discharge circuits in sync with the suction and discharge pump strokes.

Design of subsea pump 2 may be substantially not limited by compression ratio. Moreover, positive displacement control valve 30 may be configured to perform where conditions at inlet valve 21 or outlet valve 23 are above or below ambient pressures in any combination. Positive displacement control valve 30 may be operated hydraulically, electrically, or mechanically such as through a linkage to the pump drive mechanism.

Subsea pump 2 may be used to move fluid from the suction side, e.g. suction valves 31-32, to the discharge side of subsea pump 2, e.g. discharge valves 33-34. In an embodiment this process comprises fully opening the suction circuit to pump cylinders 11,13 and fully closing the pump discharge circuit during a pump suction stroke and fully closing the suction circuit, e.g. 25, and fully opening the pump discharge circuit, e.g. 26, to a downstream circuit during a pump discharge stroke.

During the pump suction stroke, fluid may be allowed to flow through pump suction port 35 into pump cylinder 13, drawing the fluid from local reservoir 100 or supply conduit by the movement of pump piston 14. Additionally, during the pump discharge stroke, fluid may be pushed within pump cylinder 13 out of subsea pump 2 by pump piston 13, allowing the fluid to exit through pump discharge port 36.

Fluid may then be pumped without the fluid passing through a valve spring loaded check valve. Exiting fluid may be routed to a different location such as pipeline 110 or a tank or the like.

In certain operations, the operation of positive displacement control valve 30 may be synchronized with the pump operation. There are various methods of synchronizing the operation of positive displacement control valve 30 with the pump operation. For example, positive displacement control valve 30 may be operated hydraulically, electrically, or even mechanically through a linkage to the pump drive mechanism. The improvements realized from the use of such positive displacement control valve 30 in pump 2 in subsea applications are independent of the particular method used to synchronize the operation with pump 2.

In certain embodiments, suction pressure may be reduced without needing to overcome a spring force in the suction check valve.

The foregoing disclosure and description of the inventions are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction and/or a illustrative method may be made without departing from the spirit of the invention.

Claims

1. A system for pumping fluids subsea, comprising:

a. a fixed displacement pump, the fixed displacement pump comprising: i. a drive cylinder, comprising a drive piston configured to be cyclically reciprocated by a separate hydraulic power unit and directional control valve; and ii. a pumping cylinder, comprising a pumping piston configured to be cyclically reciprocated by the separate hydraulic power unit and directional control valve, the drive cylinder operatively linked to the pumping cylinder;

b. an inlet valve in fluid communication with the fixed displacement pump;

c. a supply fluid line in fluid communication with the inlet valve;

d. an outlet valve in fluid communication with the fixed displacement pump;

e. a return fluid line in fluid communication with the outlet valve;

f. an actively controlled positive displacement control valve in fluid communication with the fixed displacement pump, the supply fluid line, and the return fluid line;

g. a suction line port in fluid communication with the positive displacement control valve; and

h. a discharge line port in fluid communication with the positive displacement control valve.

2. The system of claim 1, wherein the fixed displacement pump may be driven hydraulically, electrically, and/or mechanically.

3. The system of claim 1, wherein the inlet valve and the positive displacement control valve may be controlled actively and/or passively and may further be operated hydraulically, electrically, and/or mechanically.

4. The system of claim 1, further comprising an active controller operatively connected to the pump, the inlet valve, and the positive displacement control valve.

5. The system of claim 4, wherein the active controller further comprises instrumentation adapted for providing feedback to the active controller.

6. The system of claim 5, wherein the instrumentation further comprises a position sensor, a pressure sensor, a temperature sensor, a flow meter, or a sensor configured to aid in fluid qualitative analysis.

7. The system of claim 4, wherein the positive displacement control valve comprises contamination resistant, hardened metal seal elements.

8. The system of claim 1, wherein the drive cylinder is larger than the pumping cylinder.

9. A method of improving operation of a subsea pump for a subsea service, comprising:

a. disposing a pump subsea, the comprising: i. a fixed displacement pump, the fixed displacement pump comprising: 1. a drive cylinder, comprising a drive piston configured to be cyclically reciprocated by a separate hydraulic power unit and directional control valve; and 2. a pumping cylinder, comprising a pumping piston configured to be cyclically reciprocated by the separate hydraulic power unit and directional control valve, the drive cylinder operatively linked to the pumping cylinder; ii. an inlet valve in fluid communication with the fixed displacement pump; iii. a supply fluid line in fluid communication with the inlet valve; iv. an outlet valve in fluid communication with the fixed displacement pump; v. a return fluid line in fluid communication with the outlet valve; vi. an actively controlled positive displacement control valve in fluid communication with the fixed displacement pump, the supply fluid line, and the return fluid line; vii. a suction line port in fluid communication with the positive displacement control valve; and viii. a discharge line port in fluid communication with the positive displacement control valve; and

b. using the pump to move fluid from the suction side to the discharge side of the pump, moving comprising: i. during a pump suction stroke, fully opening the suction circuit to the pump cylinder and fully closing the pump discharge circuit; ii. during a pump discharge stroke, fully closing the suction circuit and fully opening the pump discharge circuit to a downstream circuit; and iii. allowing fluid to be pumped without the fluid passing through a valve spring loaded check valve.

10. The method of claim 9, further comprising reducing suction pressure without needing to overcome a spring force in a suction check valve.

11. The method of claim 9, further comprising not limiting the pump design by compression ratio.

12. The method of claim 9, wherein the subsea service comprises preventing auto-siphoning of the fluid through a chemical metering pump in applications where discharge pressure is lower than suction pressure.

13. The method of claim 9, further comprising synchronizing the operation of the positive displacement control valve with the pump operation.

14. The method of claim 9, wherein the positive displacement control valve is configured to perform where conditions at the inlet valve or outlet valve are above or below ambient pressures in any combination.

15. The method of claim 9, further comprising operating the positive displacement control valve hydraulically, electrically, or mechanically through a linkage to the pump drive mechanism.

16. The method of claim 9, wherein the subsea service comprises using the positive displacement control valve where a pressure of a subsea production is lower than the minimum possible controllable delivery pressure of a topsides metering pump.

17. The method of claim 9, wherein the subsea service comprises at least one of chemical injection into a fluid flowline, chemical metering, hydraulic fluid supply and power, pressure management, integrity testing, or blockage remediation.

18. The method of claim 9, wherein:

a. during the pump suction stroke, allowing fluid to flow through the pump suction port into the pump cylinder and drawing the fluid from a local reservoir or supply conduit by the movement of the pump piston; and

b. during the pump discharge stroke, pushing the fluid within the pump cylinder out of the pump by the pump piston and allowing the fluid to exit through the pump discharge port.

19. The method of claim 9, wherein exiting fluid it is routed to a pipeline or tank.