GB1604233A

GB1604233A - Subsea unit

Info

Publication number: GB1604233A
Application number: GB14925/77A
Authority: GB
Original assignee: Sir McAlpine Robert and Sons Ltd
Current assignee: Sir McAlpine Robert and Sons Ltd
Priority date: 1978-05-25
Filing date: 1978-05-25
Publication date: 1981-12-02

Description

(54) SUB SEA UNIT (71) We, SIR ROBERT McALPINE & SONS LIMITED, a British Company, of 40 Bernard Street, London, WC1N. 1LG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is applicable to the subsea production and initial processing of crude oil, or natural gas or other minerals such as metal ores.

The invention provides a sea bed unit for the latter purposes which is initially buoyant and can subsequently be immersed to rest on the sea bed at an offshore location and which can be recovered therefrom for installation elsewhere.

The unit comprises a concrete base carrying buoyancy control chambers and at least one concrete containment structure incorporating at least one access chamber with means permitting maintenance of a life support environment therein and an initial processing section from which initially processed mineral can be exported to a collection point or points. The containment structure is preferably spherical or cylindrical with rounded (e.g. hemispherical) domed ends. The buoyancy control chambers permit achievement of the required buoyancy while on the surface and during controlled immersion with adequate net weight when resting on the sea bed. In the latter condition it may be necessary in certain cases to provide additional fixity between the unit and the sea bed.The access chamber(s) might for example be furnished to provide a workshop and/or an equipment monitoring suite and/or temporary habitat quarters. The initial processing section will be furnished with equipment from which initally processed crude oil, gas or other mineral can be exported to a surface or shore based collection point or points. It can also be supplied with live crude oil or gas directly from one or more external sea bed wellhead installations. For the recovery of minerals from the sea bed, suction pipes or mechanical means may be employed in place of the well system.

The unit may additionally or instead have a wellhead installation embodied therein or separate and attached thereto; this would be linked through a manifold arrangement to the processing equipment housed in the unit.

The unit thus provides a compact seabed system for the production and initial processing of minerals. The seabed unit has the advantage of operation under more stable and uniform environmental conditions than floating, or semi-submersible, or other surface exposed off shore installations.

Any wellhead installation (if within the containment of the unit or within a separate nearby containment or contamments) and the process equipment zone within the unit can for example be flooded and maintained at a reduced pressure or may be filled with an inert gas at atmospheric pressure or maintained as a full habitable environment. There will preferably be access between the exterior and each of the access chamber, wellhead (if within containment) and process equipment sections directly and/or indirectly via the other sections.

The unit can be designed for complete or substantially complete assembly before towout and installation on the seabed, whereafter monitoring and control of the operation of the unit may be carried out from the access chamber or alternatively from a remote surface based facility. Manned intervention is possible within the unit, for example for completion of the hook-up operations before the commencement of operation, or for routine inspection and maintenance or in the event of breakdown during operation of the unit. Individual items of equipment may be removed and transported to a surface base for servicing and/or replacement as may be required.

Processing equipment may include manifolds, separators, pumps, compressors and other conventional plant. For oil and gas production, successive reductions in the vapour pressure of the crude mixture from the wellhead manifold allows separation of the oil and gas while impurities such as water and sand may be separated from the oil in con ventional manner.

Support facilities for the operating unit may for example include a nearby or remote platform and a semi-submersible drilling rig.

Power and control for operation of the unit may for example be supplied by seabed cable from a land source, by cable from generators (e.g. conventional gas turbines) on a floating support vessel or structure at the surface or by subsea power sources (e.g. recycle turbines or a nuclear installation). Life support back up and communications etc. for the seabed unit can be supplied and operated from a floating or fixed base.

The oil or gas or mineral produced by the seabed unit may be exported by pump ing, e.g. direct to tankers or to a storage unit or to the shore by seabed pipeline. Separated gas may be flared at the surface, used as fuel for power generation, exported or reinjected through injection wells. Separated water may be discharged to the sea or reinjected. The wellhead installation may be provided with an injection manifold.

It is envisaged that the unit may be ap plied to the recovery of offshore crude oil, natural gas or other minerals as a satellite unit feeding to a production or service platform, as a series of such units feeding to a production or service platform or as an individual unit feeding directly to land. In such a range it may be used as a mineral field extension unit or as a complete field production system. The seabed unit has the ad vantage of processing near to source but remote from a platform facility, reducing the equipment load on such a platform, reducing the number of platforms required, eliminating the need for high pressure flexible riser lines to the surface and providing an economic means of deepwater mineral process ing and recovery.

A presently preferred seabed unit suitable for crude oil and associated natural gas pro duction according to the invention, will now be described by way of example only, with reference to the accompanying drawing, in which the single Figure is a schematic pers pective view, with parts cut away, of an operating unit according to the invention.

The unit illustrated in the accompanying drawing has a closed concrete containment vessel 2 which is cylindrical in shape with domed ends and sits on a concrete base 4.

Buoyancy tanks 6 stand on the base 4 along either side of the vessel 2; these are filled with air to give additional buoyancy to the unit when it is floated to its intended site, and are flooded in controlled fashion when the unit is submerged to the seabed. The containment vessel 2 has an access chamber or section 8 which can be maintained as a full living environment and which can for example house workshop facilities, monitoring equipment, and/or temporary accommodation. Separated from the access chamber 8 by a bulkhead is a processing facility 10 for the initial processing of live crude oil or gas. The live crude oil or gas will be supplied to this processing facility via flow lines 12 from nearby seabed wellhead installations. The initially processed oil and/or gas is exported, e.g. to the shore, to the surface, or to a remote platform, by export flow lines 14.As previously indicated, the processing equipment can include means for reducing the pressure and temperature of the flow from the wellheads, for separating gases from solids and liquids, and for separating water and solids such as sand from the oil. The resulting initially processed oil and gas can then be exported safely by flow line over relatively long distances. The interior of the processing section 10 will for example be filled with an inert gas at one atmosphere pressure. Access to the interior of the unit from the surrounding water is provided at 16; the access to the access chamber 8 will be principally for manned intervention, whereas the access direct to the processing section 10 may be adapted to permit the transfer of items of processing equipment.

WHAT WE CLAIM IS:- 1. A unit for the initial subsea processing of minerals which is initially buoyant and can be or is immersed to rest on the sea bed and comprises a concrete base carrying buoyancy control chambers and at least one concrete containment structure incorporating at least one access chamber with means permitting maintenance of a life support environment therein and an initial processing section from which initially processed mineral can be exported to a collection point or points.

2. A unit according to claim 1, for the initial processing of natural gas and/or mineral oil, having supply pipes for the supply thereto of live crude oil and/or gas directly from one or more external seabed wellhead installations.

3. A unit according to claim 1 or 2, for the initial processing of natural gas and/or mineral oil, having a wellhead installation embodied therein or separate and attached thereto, the wellhead installation being linked through a manifold to the processing equipment housed in the unit.

4. A unit according to claim 3 wherein the wellhead installation has an injection manifold.

5. A unit according to any of claims 2 to 4 wherein the initial processing equipment includes manifolds, separators, pumps and compressors.

6. A unit according to claim 1, for the recovery and initial processing of solid min erals from the seabed, having suction pipes or mechanical collectors for winning the min

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sand may be separated from the oil in con ventional manner. Support facilities for the operating unit may for example include a nearby or remote platform and a semi-submersible drilling rig. Power and control for operation of the unit may for example be supplied by seabed cable from a land source, by cable from generators (e.g. conventional gas turbines) on a floating support vessel or structure at the surface or by subsea power sources (e.g. recycle turbines or a nuclear installation). Life support back up and communications etc. for the seabed unit can be supplied and operated from a floating or fixed base. The oil or gas or mineral produced by the seabed unit may be exported by pump ing, e.g. direct to tankers or to a storage unit or to the shore by seabed pipeline. Separated gas may be flared at the surface, used as fuel for power generation, exported or reinjected through injection wells. Separated water may be discharged to the sea or reinjected. The wellhead installation may be provided with an injection manifold. It is envisaged that the unit may be ap plied to the recovery of offshore crude oil, natural gas or other minerals as a satellite unit feeding to a production or service platform, as a series of such units feeding to a production or service platform or as an individual unit feeding directly to land. In such a range it may be used as a mineral field extension unit or as a complete field production system. The seabed unit has the ad vantage of processing near to source but remote from a platform facility, reducing the equipment load on such a platform, reducing the number of platforms required, eliminating the need for high pressure flexible riser lines to the surface and providing an economic means of deepwater mineral process ing and recovery. A presently preferred seabed unit suitable for crude oil and associated natural gas pro duction according to the invention, will now be described by way of example only, with reference to the accompanying drawing, in which the single Figure is a schematic pers pective view, with parts cut away, of an operating unit according to the invention. The unit illustrated in the accompanying drawing has a closed concrete containment vessel 2 which is cylindrical in shape with domed ends and sits on a concrete base 4. Buoyancy tanks 6 stand on the base 4 along either side of the vessel 2; these are filled with air to give additional buoyancy to the unit when it is floated to its intended site, and are flooded in controlled fashion when the unit is submerged to the seabed. The containment vessel 2 has an access chamber or section 8 which can be maintained as a full living environment and which can for example house workshop facilities, monitoring equipment, and/or temporary accommodation. Separated from the access chamber 8 by a bulkhead is a processing facility 10 for the initial processing of live crude oil or gas. The live crude oil or gas will be supplied to this processing facility via flow lines 12 from nearby seabed wellhead installations. The initially processed oil and/or gas is exported, e.g. to the shore, to the surface, or to a remote platform, by export flow lines 14.As previously indicated, the processing equipment can include means for reducing the pressure and temperature of the flow from the wellheads, for separating gases from solids and liquids, and for separating water and solids such as sand from the oil. The resulting initially processed oil and gas can then be exported safely by flow line over relatively long distances. The interior of the processing section 10 will for example be filled with an inert gas at one atmosphere pressure. Access to the interior of the unit from the surrounding water is provided at 16; the access to the access chamber 8 will be principally for manned intervention, whereas the access direct to the processing section 10 may be adapted to permit the transfer of items of processing equipment. WHAT WE CLAIM IS:-

1. A unit for the initial subsea processing of minerals which is initially buoyant and can be or is immersed to rest on the sea bed and comprises a concrete base carrying buoyancy control chambers and at least one concrete containment structure incorporating at least one access chamber with means permitting maintenance of a life support environment therein and an initial processing section from which initially processed mineral can be exported to a collection point or points.

erals and means for feeding the latter to the initial processing equipment.

7. A unit according to any of daims 1 to 6 wherein the or each containment structure is cylindrical with rounded domed ends.

8. A unit according to any of claims 1 to 7 wherein there is access between the exterior and each of the access chamber, the process equipment section, and any wellhead installation within the containment structure, directly and/or indirectly via another section.

9. A unit for the initial subsea processing of minerals, the unit being substantially as hereinbefore described with reference to the accompanying drawings.