SUBSEA PUMPING SYSTEM
The invention concerns a subsea pumping system that comprises an reciprocating pump such as a membrane pump or a hose pump. The motive fluid for the pump is obtained from one of the well fluids which is pressurized in a separate stage.
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The present invention relates to a pumping system for use in a remote location such as a subsea hydrocarbon extraction facility, comprising a source for high pressure fluid and a fluid driven pump.
In many fields, the pressure of the hydrocarbon reservoir will decrease as the reservoir gets depleted. Therefore, to enable increased recovery of hydrocarbons, there has been an increased use of boosting equipment. One example of this are gas lift systems. Another is the so-called ESP's that is electrical submersible pumps that are suspended in a hydrocarbon well to boost the pressure and enable hydrocarbons to be lifted to surface. The drawback of such installations is that each well needs a pump with the associated power supply and control system. Another drawback is that only liquid pumps are feasible in this situation since compressors are more difficult to operate in wells.
There is therefore an increased interest in locating the boosting equipment on the seabed and pump well fluids collected from several wells. This also enables the use of separators so that each phase of the well fluids (gas, oil or water) can be separated from each other and transported to different locations. For example can water be separated out from the well stream and reinjected into the ground, thus saving space and treatment equipment on the platform.
Added to this is the fact that new fields are found in deeper waters and further from land. This requires long step out systems for power supply and control.
Many subsea process plants with process boosting require more pumps in addition to a main booster. Traditionally, subsea pumps are large, heavy and complex units that also require electric power supply and barrier oil supply provided over a long distance. The electric system itself is highly complicated and costly, including for example penetrators, connectors, cable, transformers and motor control systems. If the host for electric power and barrier oil is a vessel or a platform, the pump supply systems will occupy highly valuable deck-area
Hydrocarbons coming from wells can be divided into several types, having mainly gas with some water or oil, having mainly oil with some water. In some instances there may be three phases, gas, oil and water. The well stream is separated into separate phases in a separator. The water may preferably be injected back into the formation.
In applications with several separation stages, the separated process medium at the later stages must be commingled with the separated process medium at first stage.
Since the process medium looses pressure throughout the separation stages, the later stages separated process medium must be boosted to reach the pressure of the first stage separated process medium. One current solution for boosting the pressure of the later stage separated process medium is to use an ejector that uses another pressurized medium as motion fluid. However, the ejector solution has the disadvantages of low efficiency and mixing of motion fluid with the driven medium.
Conventional centrifugal or screw pumps have a limited tolerance to sand. Current solution is either to let the sand go through the pump and use very high grade materials and coatings, or if the sand production is very high, the sand can be separated out upstream the pump and bypassed by means of an ejector. This ejector system is rather complex and require high flow of motion fluid.
It is therefore a need for a different solution to boost a fluid subsea.
The aim of the invention is to provide a simpler system that does not require dedicated supply of utilities (e.g. electric power and barrier fluid) from an external host, and hence will be more or less autonomous. It is also an aim of the invention to provide a system that is robust to sand and capable of pumping viscous sand slurries. This is achieved by using a subsea available pressurized fluid as a motive fluid for the pump, that the pump is a reciprocating pump and that it comprises means for creating pressure pulses in the motive fluid for operation of the pump.
The working principle of the autonomous pump invention is to bleed off some process fluid from a high pressure space to a low pressure space. In the bleed-off line it shall be fitted a valve, or arrangement of valves (hereafter named sequencing valve) which working task is to transform a steady fluid pressure to a pulsating fluid pressure for excitation of a reciprocating or oscillating pump.
Preferably the reciprocating pump is a piston type, diaphragm type or hose diaphragm type. Especially diaphragm pumps and hose diaphragm pumps are robust to sand and particles.
The means for providing the reciprocating driving fluid is a sequential valve, preferably a rotating valve or a shuttle valve. It can also be an arrangement of several valves. One sequencing valve (or valve arrangement) can be made to operate one single pump or multiple pumps.
In one embodiment of the invention where there is sand in the well fluids, the sand is separated out in a de-sander and pumped using the reciprocating pump while the clean fluid is used as the motive fluid for the pump.
In one embodiment where the hydrocarbons are mainly gas, the motive fluid is gas that is pressurized in a compressed and the compressed gas is used as the motive fluid to power the pump for the liquid phase.
In another embodiment the hydrocarbons are mainly liquids. The hydrocarbons are separated into an oil phase and a water phase. The oil phase can then be used as the motive fluid to increase the pressure in the water line to enable reinjection of water into the formation. Or vise versa, pressurized water for water injection can be used as motive fluid for increasing the oil pressure for transport to an oil-reception facility.
The invention shall now be described with reference to the accompanying drawings where
Referring first to
The high pressure fluid can be served from a remote facility. Reference can here be made to NO patent 323785 that describes a method for generating electricity in a subsea station. The high pressure fluid may be an injection fluid that is transported from a land based facility that pressurizes the fluid to a higher pressure than what is needed for the well and the excess energy/pressure is drawn from this fluid.
In
The first and second phases may be recombined downstream of the pump(s). In this case it is advantageous to pressurize the second phase to a higher pressure than the first phase, to facilitate recombination.
In
In
At times well fluids may contain particles such as sand. The sand can be very abrasive and it is normally not desirable to have sand in contact with rotary equipment, such as rotary pumps, since it can wear out the pump impellers and dynamic seals and bearings very quickly. Diaphragm pumps and hose diaphragm pumps are far more tolerant of particles since they do not have rotating parts, dynamic seals or bearings. In
In
In
Another kind of valve that may be used is the kind called a shuttle valve. Also other types of valves and valve-arrangements may be fit for purpose.
To achieve a fully functional system there must be a set pressure differential between the pump strokes. The maximum discharge pressure is set by the process pressure supplied to autonomous pump drive in displacing sequence. This pressure can be increased by increasing main booster discharge pressure, e.g. by means of a restriction at main booster discharge, downstream the branch-off to autonomous pump drive.
The pump charging sequence requires a positive differential pressure between pumped medium in pump chamber and pump drive medium. This differential pressure can be increased either by increasing suction pressure to autonomous pump (e.g. by increasing liquid column upstream pump), or by decreasing drive medium pressure.
One method of achieving this is to increase pulsation pressure negative amplitude by creating low pressure discharge by means of a venturi arrangement. Pulsation pressure negative amplitude can also be increased by means of an ejector incorporated in the sequencing valve or sequencing valve arrangement.
By adjusting the restriction it will be possible to maintain the correct pressure differential between the high pressure and the low pressure. This pressure differential can therefore be used to control the sequential valve. By adjusting the restriction the system will be able to handle changes in the composition of the well fluids.
A charging sequence may be determined by the pressure on the pump inlet. If flow should be regulated, initially the frequency on the valve must be regulated. However there is a possibility to achieve a self-regulating pump for compressor applications as the liquid column in the separator would determine how much the pump will be filled during a “charging” sequence.
The invention has been described with reference to some embodiments. A person skilled in the art will realize that there are several other ways of utilizing the invention. The reciprocating pump can for example be used for in a circuit for supplying cooling fluid to a compressor. It can also be used to set up a high pressure stream to purge a separator of accumulated sand. Also, more than one pump can be installed in the system. In the case of having more than one pump it is preferable to control both pumps with one single sequential (rotating) valve.
Claims
1. A subsea pumping system for use in a remote location such as a subsea hydrocarbon production facility, the subsea pumping system comprising:
- a source of high pressure fluid; and
- a fluid driven reciprocating pump;
- wherein the high pressure fluid is used as a motive fluid for the pump; and
- means for creating pressure pulses in the motive fluid.
2. The subsea pumping system according to claim 1, wherein the source of high pressure fluid is produced gas pressurized by a compressor.
3. The subsea pumping system according to claim 1, wherein the source of high pressure fluid is produced liquids pressurized by a liquid pump.
4. The subsea pumping system according to claim 1, wherein the source of high pressure fluid is an injection fluid provided by a pump located at a topside facility.
5. The subsea pumping system according to claim 1, wherein the reciprocating pump is a diaphragm pump.
6. The subsea pumping system according to claim 1, wherein the reciprocating pump is a hose diaphragm pump.
7. The subsea pumping system according to claim 1, wherein the reciprocating pump is a piston pump.
8. The subsea pumping system according to claim 1, wherein the means for creating pressure pulses comprises at least one valve arranged between the source of high pressure fluid and the pump.
9. The subsea pumping system according to claim 8, the means for creating pressure pulses comprises an inlet valve and an outlet valve which are synchronized to provide the pulses.
10. The subsea pumping system according to claim 8, wherein the means for creating pressure pulses comprises a rotating sequencing valve.
11. The subsea pumping system according to claim 10, wherein the rotating sequencing valve has a rotational axis which is parallel to a pipeline axis for a pipeline in which the valve is arranged.
12. The subsea pumping system according to claim 1, further comprising at least one separator.
13. A method for operating a subsea reciprocating pump, the method comprising the steps of:
- separating out a first fluid phase from a well stream comprising a plurality of phases;
- increasing the pressure of said first fluid phase; and
- using a portion of the pressurized first fluid phase as a motive fluid for the reciprocating pump.
14. The method according to claim 13 wherein the pressurized first fluid phase is fed to the reciprocating pump through a sequential valve.
15. The method according to claim 13, further comprising the step of the regulating a pressure differential in the first fluid phase.
16. The subsea pumping system according to claim 10, wherein the rotating sequencing valve has a rotational axis which is transverse to a pipeline axis for a pipeline in which the valve is arranged.
Type: Application
Filed: Oct 29, 2010
Publication Date: Nov 8, 2012
Applicant: FMC Kongsberg Subsea AS (Kongsberg)
Inventor: Leif Arne Tønnessen (Baerums Verk)
Application Number: 13/504,931
International Classification: F04B 47/08 (20060101);