NO20140542A1 - Pump system for water injection at high pressure - Google Patents

Abstract

The invention provides a pump system for high pressure water injection, which will comprise at least two units with water injection pumps connected in series, each pump unit comprising an engine in an engine compartment which will be operatively coupled to operate a pump in a pump compartment, characterized in that the engine compartment for at least the pump units coming after the first pump unit will be sized according to a lower pressure class than the operatively connected pump room. Method of arranging said system and use of said system.

Description

PUMP SYSTEM FOR WATER INJECTION AT HIGH PRESSURE

Field of the invention

The present invention relates to water injection into underground reservoirs under water, such as to stimulate production from a reservoir containing petroleum.

Background of the invention and prior art

Water injection to stimulate production from a petroleum reservoir takes place by pumping water at high pressure into injection wells. The high-pressure water is pumped into that reservoir, or into the formation that is in fluid communication with the reservoir. In this way, the reservoir pressure will be able to be maintained, and petroleum will be able to migrate towards the production wells.

In order to obtain sufficient pressure from underwater pumps, a number of pumps can be arranged in series. However, the pressure will increase for each pump unit, and subsequent pump units will then be exposed to the full pressure from the upstream pump stage, where the pressure will have increased for each pump stage or for each pump unit. Each pump stage or each pump unit will comprise a motor and a pump which will be connected together inside a housing.

A typical assessment for design, operation and maintenance would be to have one type of pump unit in all stages. The pressure housing must be selected so that the last pump stage, or the maximum pressure to which the pumps will be exposed, will govern the selection. Consequently, all pump units will be able to have the same pressure housing, which will lead to heavy and expensive pump units, but offers simplifications with regard to the storage of spare parts and maintenance.

Alternatively, the pressure housing classification could increase for each pump step, but this would have the effect that the pump units with a lower pressure housing classification would not be able to be replaced with pump units that have a higher pressure housing classification. The effect will either be that the total weight of the pump system will be able to weigh several tonnes more than what would have been necessary and will cost millions in excess, or that millions in excess will have to be spent on extra spare parts. There will be a demand for a pumping system that will not have such disadvantages as mentioned above.

Summary of the invention

The demand will be able to be met with the present invention.

More specifically, the invention will provide a system of high-pressure pumps for water injection, comprising at least two pump units for water injection, which are connected in series, where each pump unit will comprise a motor in an engine compartment which will be operatively connected to operate a pump in a pump room, characterized by the fact that the engine room for at least the pump units that follow the first pump unit will be dimensioned according to a lower pressure class than the operationally connected pump room.

The term high-pressure water injection system means that at least two pumps for water injection must be arranged in series in order to achieve the desired pressure.

For the pump units that come after the first pump unit, the engine compartment pressure housing will preferably be dimensioned for the same pressure as the pressure housing of the first pump. More preferably, all engine compartment pressure housings will be sized for the same pressure class. The effect of this will be that the pressure housing or pressure shell for the pump rooms will be thinner and lighter, and that, in addition, associated equipment, such as penetrators, sensors and flanges, will be dimensioned for a lower differential pressure.

For the pumps that come after the first pump unit, the engine compartment's pressure housing will preferably be dimensioned for the same pressure as will be for the pressure housing of the first pump (depending on the maximum supply pressure for the engine's system with barrier fluid, this could be higher than the pump's suction pressure). If the inlet pressure for the first pump is the same as the pressure from the surrounding seawater, or somewhat less than this (depending on pipelines and any potential water treatment facility upstream of the injection pumps), that is, the inlet will be raw or treated seawater, the same class will for excess pressure in the pressure housing of the engine compartment should preferably be selected for all engine compartment housings. Said overpressure will typically be 10-20 bar overpressure during operation, but the pressure classification for the engine compartment should be equal to the maximum supply pressure for the barrier fluid system, which will typically be approximately 50-100 bar above the pressure in a throttling chamber, as will be described below.

In a preferred embodiment, a leakage seal could be arranged between the pump room housing and a throttling chamber, the throttling chamber would be for each pump unit that comes after the first pump unit arranged between the pump and the engine rooms, and each throttling chamber would be connected to a leakage line that would be connected to the inlet line for the first pump. More preferably, a leak seal will be provided between the pump room housing and a choke chamber, the choke chamber will be for each pumping unit located between the pump and the engine compartments, and each choke chamber will be connected to a leak line which will be connected to the inlet line of the first pump. For some embodiments, preferably embodiments that use raw seawater or treated seawater as injection water, the exhaust line will be looped and the flow that is leaked to the choke chamber will be released to the sea.

More specifically, each throttling chamber may include a throttling seal in a partition wall to the pump room, the throttling seal may be a labyrinth seal or any type of mechanical seal that has a throttling or leakage effect, such as a spring loaded mechanical seal where the spring will be able to adjust the leakage opening , preferably a regulated or an adjustable throttling effect, and a more fluid-tight mechanical seal (very small leakage, typically a few liters per day during normal operation) will be able to be arranged in the partition between each throttling chamber and engine compartment. The fluid-tight seal between the throttling chamber and the engine compartment will preferably be able to be connected to a barrier fluid system at a pressure that will be the same as or higher than the pressure that will be in the throttling chamber. The barrier fluid pressure in the engine will be able to be controlled by a pressure-volume regulator (PVR).

In a preferred embodiment, seawater will be able to be used as a cooling medium for the engine, where the seawater will be provided by at least one separate cooling pump for seawater, and which has been arranged to pump seawater through the engine compartments. Even more preferably, seawater could be used as a coolant for the engine, provided by the injection water to cool the leak through a choke or leak seal provided in the partition wall between the pump and the engine compartments, said seal could be a labyrinth seal or any type of mechanical seal which has a throttling or leakage effect, such as a spring-loaded mechanical seal, preferably the leakage sealing rate will be proportional to that which will be required by the engine cooling. A fully insulated motor will be decisive for reliability for those designs that use seawater or injection water as a cooling medium. Insulation materials, such as cross-linked polyethylene XLPE, or PEEK or something else, could be used. For the embodiments that pump in seawater for use as coolant in the engine, the vanes on the seawater engine will preferably be arranged on the engine shaft.

Typical pressure classes for pump rooms could be 5000 psi (345 bar), 10000 psi (690 bar), 150000 psi (1035 bar) and 20000 psi (1380 bar). Typical pressure classes for the engine compartment will be significantly lower, for example 100 bar or less.

The invention will also provide a method to be able to arrange a pump system for high-pressure water injection, which comprises at least two pump units for water injection connected in series, where each pump unit will be comprised of a motor in an engine compartment that is operatively connected to be able to operate a pump in a pump room. The procedure will be characterized by the fact that the engine compartment for at least the pump units that follow the first pump unit will be dimensioned according to a lower pressure class than the operationally connected pump compartment, more preferably the engine compartment's pressure housing for the pump units that come after the first pump unit will be dimensioned for the same the pressure that is in the pressure housing for the first pump, most preferably all pressure housings for the engine compartment will be dimensioned for the same pressure class.

In addition, the invention will provide an application of a pump system for high-pressure water injection according to the invention, for injecting water at high pressure into an underground reservoir under water.

Figures

The invention has been illustrated with seven figures, of which:

Figures 1 a and 1 b illustrate embodiments of a pump system according to the invention, with pump units that will not be identical, Figures 2 a and 2 b illustrate embodiments of a pump system according to the invention, with pump units that will be identical, Figures 3 a , 3 b, 3 c and 3 d illustrate embodiments of a pump system according to the invention, which uses sea water or injection water as cooling medium.

Detailed description

Reference will be made to fig. 1, which illustrates an embodiment of a pump system according to the invention, where the first pump unit will be different from the second and subsequent pump units. More specifically, the first pump unit will have no choke chamber, thus no choke seal between a pump room and choke chamber and no leakage line connected to a choke chamber. This will give an advantage of not having any loss due to leakage in the first pump, and thus a somewhat better efficiency. In addition, it will be possible to use a shorter and thus a stiffer axle. On the other hand, this embodiment will have the disadvantage that the operator will then have two different versions of pumps and will have to have extra spare parts and procedures for maintenance. An alternative embodiment, but with a leak to the sea and therefore no leak line, will be illustrated in figure lb.

Reference will be made to fig. 2 a, which illustrates an embodiment of a pump system according to the invention, where all the pump units will be identical. For this embodiment, a choke chamber will be provided between the pump room and engine room for all pump units, a leak line will be from each choke chamber to the inlet of the first stage and a choke seal will be provided on the shaft which is between each pump room and choke chamber. Consequently, it will be possible to allow flexibility and fewer spare parts, but then at the expense of a somewhat lower degree of efficiency, due to the leakage current that is above a throttle seal, also for the first-stage pump. An alternative embodiment, but with a leak to the sea and thus no leakage line, will be illustrated in figure 2 b.

The leakage over the throttling seal and the leakage line will be dimensioned to avoid an overpressure in the throttling chamber. Dimensioning for the leakage line must take into account that the maximum flow rate will be proportional to the square of the flow rate. However, an opening for a relief valve at an intended pressure could be arranged in the throttling chamber.

Another embodiment would be to use the pumped medium as a stream of coolant for the engine. In this configuration, the leakage flow will be able to be routed from the pump through the motor and either be discharged to the sea (Fig. 3 c), or be routed back to the inlet of the first pump to recover the pumped fluid (Fig. 3 d). The advantage of this embodiment will be that the injection pump itself will generate the necessary differential pressure across the leakage seal between the pump and engine compartment. The leakage seal will then be able to be designed so that a sufficient flow rate is achieved to be able to cool the engine without the use of an additional circulation impeller for the cooling fluid in the engine. As the speed of the pump / motor is increased, the injection pump will be able to generate an increasing differential pressure across the leak seal, and thus the flow rate, to provide sufficient cooling of the increasing motor loss at higher rotational speeds. This will mean that the typical characteristic of flow against pressure in the leak seal between the pump and engine compartment will be able to be designed to provide sufficient cooling flow through the engine at any speed.

In alternative embodiments, the engine could be cooled by using a pump that extracts seawater from the environment (raw seawater or seawater that has been somewhat treated) or from the same or another underwater water treatment system and be released back to the inlet line (Fig. 3) a) or released into the sea (Fig. 3 b).

Which of the illustrated embodiments are to be preferred in each case will be able to be estimated by making use of a good practice of the technical and for calculating the costs. The embodiments that use the pumped fluid as a coolant, the injection water, will often be the most preferred embodiment since no barrier fluid system will be required, and the cooling will be able to be adjusted to the cooling demand since the seal leakage rate will be able to be designed to meet for the engine's need for cooling. However, each of the embodiments will be able to lead to significant simplifications and savings compared to the pump systems that are of the prior art for high-pressure water injection, since the pressure class for parts of the system will be able to be significantly reduced, with consequent savings in weight, costs, stock of spare parts for the pumps and associated equipment such as penetrators. The cost savings could amount to millions of Norwegian kroner, and the weight savings could be counted in metric tonnes.

Claims (11)

1. Pump system for high-pressure water injection, which will comprise at least two units of water injection pumps connected in series, where each pump unit will comprise an engine in an engine compartment which will be operatively connected to operate a pump in a pump compartment, characterized by at least the pump units that come after the first pump unit will be comprised of a throttling chamber arranged between the pump and the engine compartments, a leakage seal arranged between the pump and the engine compartments, where the throttling chamber has an outlet, and that engine compartment for at least the pump units that come after the first pump unit will be dimensioned according to a lower pressure class than the operationally connected pump room. 2. Pump system for high-pressure water injection according to claim 1, characterized in that, for the pump units that come after the first pump unit, the engine compartment's pressure housing will be dimensioned for the same pressure as will be in the pressure housing for the first pump. 3. Pump system for high-pressure water injection according to claim 1, characterized by the fact that all pressure housings for engine compartments will be dimensioned for the same pressure class. 4. Pump system for high-pressure water injection according to claim 1, 2 or 3, characterized in that each throttling chamber will be connected to a leakage line which will be connected to the inlet line for the first pump. 5. Pump system for high-pressure water injection according to claim 1, 2 or 3, characterized in that a leak seal will be arranged between the pump room housing and a throttling chamber, where the throttling chamber will, for each pump unit that comes after the first pump unit, be arranged between the pump and the motor chambers , and each choke chamber will be connected to a leak line connected to the inlet line of the first pump. 6. Pumping system for high pressure water injection according to claim 4 or 5, characterized in that each throttling chamber includes a throttling seal in the partition wall towards the pump room, the throttling seal will be a labyrinth seal or any type of mechanical seal that has a throttling or leakage effect, such as a spring-loaded mechanical seal where the spring adjusts the leakage opening, preferably a regulated or an adjustable throttling effect, and a fluid-tight mechanical seal will be arranged in the partition between each throttling chamber and engine compartment. 7. Pumping system for high-pressure water injection according to claim 1, 2 or 3, characterized in that seawater will be used as coolant for the engine, the seawater will be provided by at least one separate cooling pump for seawater being arranged to pump seawater through the engine compartments, preferably the seawater pump will be arranged as a seawater pump impeller on the motor shaft. 8. Pump system for high-pressure water injection according to claim 1, 2 or 3, characterized in that injection water will be used as a coolant for the engine, provided by injection water for cooling that leaks out through a throttle or a leak seal arranged in a partition between the pump and the engine compartments, said seal could be a labyrinth seal or any type of mechanical seal that has a throttling or leakage effect, such as a spring-loaded mechanical seal, preferably the seal leakage rate will be proportional to the cooling requirement of the engine. 9. Procedure for arranging a pump system for high-pressure water injection, which will be comprised of at least two pump units for water injection connected in series, where each pump unit will comprise an engine in an engine compartment which will be operatively connected to operate a pump in an engine compartment, characterized by providing, for at least those pump units following the first pump, a throttling chamber between the pump and the engine compartments, a leakage seal between the pump and the throttling chamber, and an outlet from the throttling chambers; and size the engine room, for at least the pump units that come after the first pump unit, according to a lower pressure class than the operationally connected pump room, more preferably the engine room pressure housing of the pump units that come after the first pump unit will be sized for the same pressure which will be for the pressure housing of the first pump, most preferably all pressure housings for the engine compartment will be dimensioned for the same pressure class. 10. Use of a high pressure water injection pump system according to any one of claims 1-8 or 11, for injecting water at high pressure into an underground reservoir under water. 11. Pump system for high-pressure water injection, which will be comprised of at least two pump units for water injection connected in series, where each pump unit comprises a motor in an engine compartment which will be operatively connected to operate a pump in a pump compartment, characterized in that it includes a leak seal which is arranged between the pump and the engine compartments, the engine compartment has an outlet and will be cooled by the leaked water and possibly by added seawater, and preferably the engine compartment for at least the pump units that come after the first pump unit will be dimensioned according to a lower pressure class than the operationally connected pump room.