GB2550325A

GB2550325A - Subsea seabed power generation system and chemical inhibitors storage and injection

Info

Publication number: GB2550325A
Application number: GB1606778.7A
Authority: GB
Inventors: Singh Johal Kashmir
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-04-16
Filing date: 2016-04-16
Publication date: 2017-11-22
Anticipated expiration: 2036-04-16
Also published as: GB2550325B

Abstract

A system for generating electrical power on the seabed from the potential energy of water between sea surface 1 and seabed 2, using a water turbine 5, an electrical generator 6, and a power converter 7, and additionally having a water injection system. The generated electricity is used for providing power to a subsea oil or gas field, or can be distributed to other undersea uses or onto land for commercial or domestic use via a power umbilical cable 8. Alternatively the power can be converted into mechanical energy to drive fluid pumps for the subsea oil and gas fields. Sea water is used to inject into an oil or gas reservoir 10 via a water injection tree 9 for pressure maintenance and production enhancement. The injection system may be a Raw Water Injection (RWI) system 3 for cleaning seawater before injection. They may be a water injection pump 4. There may be more than one turbine, arranged in a series or in parallel. There may be more than one well water injection system. There may be facilities for the storage and injection of chemical inhibitor fluids.

Description

SUBSEA SEABED POWER GENERATION SYSTEM and CHEMICAL INHIBITORS STORAGE AND INJECTION DESCRIPTION:

Currently the electrical power that is required for subsea oil and gas fields to operate equipment such as Valves, Pumps, Compressor’s etc. is obtained from either surface facilities or onshore via a power umbilicai. This can in some instances be cost prohibited.

In this invention a method of generating subsea power is presented for the following potentiai uses: • Enhancing oil and gas field production. • Providing locai power subsea to production and injection equipment such as valves, pumps compressors etc. • Transporting excess power to other oil and gas fields and onshore for commercial and domestic use. • Storage of eiectrical power subsea. • Providing mechanical drive power for production fluids pumping for pressure boosting on the seabed. • The deployment of chemical inhibitors storage and inject facilities on the subsea seabed.

According to this invention the energy from the static head pressure from sea surface (1) and the sea bed (2) of sea water is captured and the sea water is used to inject into a convenient reservoir (10) via water injection tree (9) (see Fig. 1) for oii and gas fieid pressure maintenance and production enhancement. Alternatively the water can be injected into a locai aquifer if present. The excess pressure avaiiable at the sea bed is diverted to a water turbine(s) which either drives an electrical generator or is used to drive a production or inject pump having wet gas, liquids or multiphase fluids.

The proposed subsea power generation system can include the following items of equipment (Fig. 1): • A raw water injection (RWI) system (3) in order to clean the sea water to the required specification for injection into the oil or gas reservoir. If sea water can be injected into the reservoir without the need for its processing then a RWI system will not be required. • A water injection pump (4) if required. A pump will normally not be required for the majority of applications. • A water turbine(s) (5) for energy conversion. • An electric generator (6) for harvesting free or waste energy from the surrounding seawater using water turbines. • Electrical transformers (7) as required for the desired application. • A method of electrical energy storage if required. • A power umbilical (8) to transport the generated electrical energy to either nearby oil and gas fields, vessels or to onshore if economical.

The current state of technology for water turbines is limited to differential pressures of 500-1000m head. Therefore for deep water applications a number of turbines will need to be placed in series or parallel in order to limit the differential pressures to each turbine.

Figure 2 and 2a shows a three turbine system in series and parallel injecting into a four well water injection system. The Raw Water Injection system (11) which includes filters and other associated equipment processes the sea water. The processed sea water passes through each turbine / electricity generator system (12) and then diverted to each water injection tree (14) to the supply the reservoir (15). A control system (13) is deployed via the use of control valves to restrict the sea water pressure head to each turbine unit.

The generated electricity (16) from each generator is the transmitted to the required location/s. An electrical energy storage device (17) is used for system start-up or black start conditions.

Figure 2b shows an arrangement in which the water turbine (12) is used to drive a production fluids pump fluids (17). The production pump can be either a liquids only (Oil and Water), multiphase fluids (Oil, Gas and Water) or a wet gas compressor.

This will enable the long distance of production fluids transport. In this arrangement the kinetic energy of the injection water is converted to mechanical energy to drive the production fluids pump and no electric energy is generated.

In practice for an oil and gas field development a combination of electrical and mechanical energy generation will need to be deployed. This will enable the oil and gas field to be serviced locally without the requirement of topsides equipment or power.

Figure 2c shows an arrangement and facilities for the storage and injection of chemical inhibitor fluids from the seabed. The principle consists of cylinders (11), (12), (13) and (20) that are made up of a ram cylinder mechanism that contain the chemical inhibitor fluids (19). The piston has a leak system to avoid the mix of sea water and the chemical inhibitor.

For deep water depth oil and gas fields, the pressure due to the water static head can be between 200bara to SOObara for water depths between 2000m and 3000m of respectively. This pressure is used to drive the chemical inhibitor fluids into the production flow path with a pressure differential across the piston (sea water and production pressure).

The storage and injection system is as follows: • Hydrate Inhibitor Injection Into the Well(2): Tanks (11) is used to inject hydrate inhibitor fluid into the Well between Master and Gate valves (4) and (5) and injection valve (22), during a shutdown of the facilities or prior to startup. Tanks (12) are spare inhibitor storage. A pump (18) may be used if sea bed pressure is lower than required and with the electrical power available from the above described system. The injection rate is measured via the venture meter (14). The same system can be used to inhibit the jumper prior to start-up of the production system. • Hydrate Inhibitor injection into the Manifoid (9): A similar arrangement is available for injection into the manifold system using tanks (20) and associated flow measurement meter (16) and injection vaive (10). • Corrosion and Scale Inhibitors in the Pipeline system: These inhibitors can be cocktaiied and injected via tanks (13) either upstream or downstream of the production choke (6) with injection rates measured using venture meter (15) and injection valves (7) and (8). • Other Chemical Inhibitors: The same system arrangements can be used for additional chemical inhibitors.

The chemical inhibitor storage volume is economically designed to enable minimal intervention to replace injected chemicals. This is undertaken via the use of Remote Operated Vehicles (ROV) which can be docked into the storage tanks (21).

Note that if the sea water pressure is higher than the required inject pressure for the chemicals then no electrical power will be required for these operations. APPLICATIONS:

The invention presented for subsea power generation and reservoir water injection applications can be summarized but not limited to the following; • Generate electrical power locally subsea. • Distribute the generated electrical power locally to electrical equipment such as valves, pumps, compressors and other locations such as other oil and gas fields and vessels as well as onshore for domestic and commercial use. • This is an enabling technology that can be deployed for othenvise non deployable equipment subsea such as gas compression equipment. • Single and multiphase pumps can be driven by the water turbine system without generating electrical power but rather by mechanical drive system. • The ability to store and inject chemical inhibitor fluids on the seabed.

Claims

1. A system that provides a subsea power generation system, comprising: a. An energy-capturing method that harvests free pressure energy from the sea water column. b. The system comprises of a Raw Water Injection system, a water turbine and an electrical generator connected to the power converter at the subsea sea bed location.

2. The water energy is captured by a condition whereby the pressure due to the head of the water column is greater than the reservoir pressure plus the friction loss in the tubing between the sea bed and the reservoir. This excess pressure is used to drive a water turbine which in turn drives an electrical generator.

3. A power of up to 28MW can be generated (Fig. 3) if the water depth is 3000m and the reservoir is at a depth of 1000m below the sea bed for a single subsea installation.

4. The generated power can be distributed locally subsea as well as transported to other oil and gas fields or onshore for domestic or commercial use.

5. This invention provides not only electrical energy but also water to an oil or gas reservoir for pressure maintenance and enhanced production and reservoir recovery.

6. The power generated by the water injection system can also be converted into mechanical energy to drive production fluids pumps (Liquids, Multiphase and Wet Gas).

7. The sea water potential energy is further used to store and inject cherhical inhibitors into the production subsea system without requiring additional power for deep water oil and gas fields.