System and method for injecting water into an underwater hydrocarbon reservoir

Abstract

Water is supplied from a host facility (2) to a pump (10) in a seabed facility (5) via a connecting pipeline (6). The pump (10) pumps the water to a higher pressure, and injects the pumped water into a hydrocarbon reservoir at a pressure higher than the pressure of the fluid in the reservoir so that it drives production fluid there to the host facility (2).

Description

[0001] The present invention relates to a system and method for injecting water into a hydrocarbon reservoir.

[0002] In an oil and/or gas field development, production fluid, extracted from the hydrocarbon reservoir by production wells, is driven to a host facility by the natural pressure of the reservoir. However, the natural pressure varies from field to field and some reservoirs may not have enough pressure to drive the production fluid to the host facility.

[0003] A way of overcoming this problem is to boost the pressure of the reservoir by injecting water supplied from the host facility into it. A seabed facility pipeline connects the host facility to a seabed facility where the pipeline is manifolded into separate well flowlines connected to water injection wells located at the extremities of the reservoir. Water for injection purposes is normally chemically treated and filtered at the host facility to ensure its suitability for injection into the hydrocarbon reservoir. However, in some instances, dependent upon the local seawater and the particular reservoir, it may be possible to inject seawater into the reservoir without chemical treatment.

[0004] The water is pumped down the seabed facility pipeline and into the reservoir via the seabed facility, the well flowlines and the water injection wells. The injected water is pumped to a pressure higher than the natural pressure of the reservoir so that it drives production fluid from the reservoir up to the production wells and on to the host facility.

[0005] The required pressure of the injected water is typically in the region of 27.58 MPa (4000 pounds per square inch). Hence, the pipeline and flowlines which are required to convey the injected water to the injection wells have to have walls thick enough to withstand the high pressure of the water. The costs of the pipeline and flowlines themselves and the installation costs are high.

[0006] U.S. Pat. No. 4,848,471 discloses a system for injecting water into a production well. Seawater is treated and pressurised at a host facility before being transported in a supply line to drive an underwater fluid driven motor. A portion of the seawater is conveyed from the supply line for injection into the well via an injection pump driven by the motor. Return water from the fluid driven motor is carried in a separate return line back to the host facility.

[0007] It is therefore an object of the present invention to provide a system and method which overcomes at least the above-mentioned disadvantage of the prior art.

[0008] According to one aspect of the present invention there is provided a system for injecting water into a hydrocarbon reservoir, comprising a host facility having water supply means, an underwater pump remote from the host facility, and connected to the water supply means by a pipeline, and at least one water injection well connected to the underwater pump, whereby the pump is arranged to pump the water received from the pipeline to the or each well to inject the pumped water Into the reservoir at a pressure higher than the pressure of the fluid in the reservoir, characterised: in that

[0009] said underwater pump comprises an electric motor driven pump.

[0010] The pump may be connected to the at least one water injection well by at least one flowline which is able to withstand conveyed fluid of a higher pressure than the pipeline between the host facility and the underwater pump.

[0011] The pump is preferably located at an underwater facility such as a seabed facility. Gravity alone may be used to convey water to the pump at the underwater facility. In contrast, the prior art described requires the water to be pumped to the seabed facility. By locating the pump on the underwater facility, a pipeline able to convey fluid at a high pressure is not required between the host facility and the underwater facility, as water from the host facility is only at a high pressure once it has been pumped by the pump. Hence, the pipeline between the host facility and the underwater facility may have its pipe wall thickness reduced as it does not need to convey fluid at such a high pressure. As there is a reduction in the quantity of pipe material for this pipeline, there is a significant cost saving.

[0012] By conveying the water for injection at a lower pressure to the underwater facility, the pressure losses due to friction in the pipeline are reduced. Consequently, less power is required to pump the water for injection, enabling a smaller pump and drive motor (which is electric) to be specified at the underwater facility and, if required, at the host facility. Hence, there is a further cost saving as a smaller pump requires less energy to drive it. If the host facility also has a pump for water supply, the reduction in size of the pump and its associated drive motor provides a saving in deck space on the host facility and in the weight to be supported by the host facility. If water supply is by gravity alone, no pump need be provided at the host facility.

[0013] The reduction in pipe wall thickness enables the sections of the pipe for making up the pipeline to the underwater facility to be welded together more easily and quickly which considerably reduces fabrication costs. Furthermore, the reduction in pipe wall thickness may enable the pipeline to be reeled onto a drum and be laid from a pipe reel-lay barge which is a faster method of installing a pipeline than other conventional methods.

[0014] The savings in pipeline costs enables longer tie-backs to the host facility to be economically considered which may allow the use of an existing host facility to be used for a remote field as opposed to having to provide a new host facility. This is of particular benefit when the field to be developed is located beneath deep water.

[0015] The system preferably includes a power and control umbilical from the host facility to the underwater pump for conveying power and control signals to the pump. The power and control umbilical may be also arranged to convey power and control signals required for other underwater equipment such as wellhead trees and manifolds. Minimal additional cost is incurred when providing power to the underwater pump if the same umbilical is used for the underwater pump and other underwater equipment.

[0016] The underwater facility may include a retrievable module which incorporates the pump. Hence, the pump may be easily recovered for inspection, maintenance or repair, for example. The module may be of the type forming part of the modular system designed by Alpha Thames Ltd of Essex, United Kingdom, and named AlphaPRIME.

[0017] According to another aspect of the present invention there is provided a method for injecting water into a hydrocarbon reservoir, comprising the steps of supplying water from a host facility to an underwater pump via a connecting pipeline, pumping the water received by the underwater pump to a higher pressure, and injecting the pumped water into the reservoir at a pressure higher than the pressure of the fluid in the reservoir, characterised by the step of:

[0018] driving the underwater pump with an electric motor.

[0019] The method may include the steps of using any of the system components referred to above.

[0020] Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:—

[0021] FIG. 1 is a schematic diagram of a system for putting the invention into practice; and

[0022] FIG. 2 is a modified detail of FIG. 1.

[0023] Referring to FIG. 1 of the accompanying drawings, a system 1 has a host facility 2 which may be, for example, onshore or on a fixed or floating rig. The host facility 2 has an injection water treatment plant 3 with a connected pump 4 which is connected to a remote seabed facility 5 by an injection water supply pipeline 6. The seabed facility 5 is connected to a plurality of water injection wells 7 for a hydrocarbon reservoir-whereby each well is connected to the facility 5 by a separate supply flowline 8 which is able to withstand conveyed water of a higher pressure than the water supply pipeline 6.

[0024] At the seabed facility 5 the water supply pipeline 6 is connected to an inlet 9 of a high pressure pump 10 and a conduit 11 from an outlet 12 of the pump 10 is manifolded to the flowlines 8 connected to the water injection wells 7.

[0025] The pump 10 is arranged to be supplied with power and control signals from the host facility 2 via a power and control umbilical 13.

[0026] The operation of the system 1 will now be described.

[0027] The water treatment plant 3 chemically treats the water for injection so that it is suitable for injection into the hydrocarbon reservoir and the pump 4 at the host facility 2 pumps the treated water into the water supply pipeline 6 where gravity assists the conveyance of the water to the seabed facility 5.

[0028] At the seabed facility 5, the water is pressure boosted by the high pressure pump 10 and is injected into the hydrocarbon reservoir via the well

[0029] supply flowlines 8 and the water injection wells 7. The pressure of the injected water is higher than the pressure of the fluid in the reservoir so that it drives the production fluid to the host facility 2 via production wells (not shown).

[0030] A modification to the system 1 will now be described in which parts which correspond to those shown in FIG. 1 are designated with the same reference numerals and are not described in detail below. In the modified system, the seabed facility 16 illustrated in FIG. 2 comprises a base structure 17 which supports a retrievable module 18 that contains the high pressure pump 10. The pump inlet 9 is connected to the injection water supply pipeline 6 from the host facility 2 by a multi-ported fluid connector 19 such as that described in GB-A-2261271 and the pump outlet 12 is connected by the conduit 11 to the well supply flowlines 8 via the same multi-ported fluid connector 19. This connector 19 enables the module 18 to be isolated from the pipeline 6 and flowlines 8 connected to the base structure 17 when the module 18 is to be retrieved.

[0031] In addition, the module 18 has a power and control pod 20 which is connected to the power and controls umbilical 13 by a connector 21 whereby the pod 20 directs power and provides control signals to equipment within the module 18. In particular, the pod 20 controls the high pressure pump 10 but it may be overridden by control signals received from the host facility 2 via the umbilical 13. The pod 20 also drives the pump 10 with power received from the host facility 2 via the umbilical 13.

[0032] In use, water from the host facility 2 is received by the high pressure pump 10 in the module 18 via the fluid connector 19 and pressure boosted water is pumped out of the module 18 via the fluid connector 19 and manifold conduit 11 and into the hydrocarbon reservoir via the well supply flowlines 8 and water injection wells 7.

[0033] Whilst particular embodiments have been described, it will be understood that various modifications may be made without departing from the scope of the invention. For example, the pump 4 at the host facility 2 may not be required if the injection water can flow to the remote facility 5 under the action of gravity alone. The power and control pod 20 in the retrievable module 18 is also optional, as power and control could be provided/controlled externally of the module. The pipeline and flowlines described may be of rigid or flexible construction.

[0034] Although the invention has been described in the context of a subsea hydrocarbon field, it would also be applicable to other areas such as swamps whereby the system including the pump 10 remote from the host facility 2, would be land based.

Claims

1. A system (1) for injecting water into a hydrocarbon reservoir, comprising a host facility (2) having water supply means (3), an underwater pump (10) remote from the host facility (2), and connected to the water supply means (3) by a pipeline (6), and at least one water injection well (7) connected to the underwater pump (10) whereby the pump (10) is arranged to pump the water received from the pipeline (6) to the or each well (7) to inject the pumped water into the reservoir at a pressure higher than the pressure of the fluid in the reservoir, characterised in that

said underwater pump comprises an electric motor driven pump (10).

2. A system as claimed in claim 1, wherein the pump (10) is connected to the at least one water injection well (7) by at least one flowline (8) which is able to withstand conveyed fluid of a higher pressure than the pipeline (6) between the host facility (2) and the underwater pump (10).

3. A system as claimed in claim 1 or 2, wherein the pump (10) is located at an underwater facility (5).

4. A system as claimed in claim 3, wherein the underwater facility (5) includes a retrievable module (16) which incorporates the pump (10).

5. A system as claimed in any preceding claim 1, including a power and control umbilical (13) from the host facility (2) to the underwater pump (10) for conveying power and control signals to the pump.

6. A system as claimed in claim 5, wherein the power and control umbilical (13) is arranged to convey power and control signals required for other underwater equipment.

7. A method for injecting water into a hydrocarbon reservoir, comprising the steps of supplying water from a host facility (2) to an underwater pump (10) via a connecting pipeline (6), pumping the water received by the underwater pump (10) to a higher pressure, and injecting the pumped water into the reservoir at a pressure higher than the pressure of the fluid in the reservoir, characterised by the step of:

driving the underwater pump (10) with an electric motor.