Wells – Submerged well – Means removably connected to permanent well structure
Patent
1993-08-02
1995-03-21
Britts, Ramon S.
Wells
Submerged well
Means removably connected to permanent well structure
166357, 55218, E21B 4301
Patent
active
053987624
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a compressor system in a subsea station for transporting a well stream, comprising a compressor with a motor in a common drive atmosphere within a pressure shell, a gas chamber and a gas suction line between the gas chamber and an inlet in the compressor, a gas line between the gas chamber and the drive atmosphere within the pressure shell, and a lube oil circuit comprising a lube oil sump open to the drive atmosphere, a lube oil pump, bearings in the motor and compressor, and a lube oil line to the bearings.
The invention has been developed particularly in connection with the development of a subsea station for pumping a well stream. Oil and gas production at sea usually takes place today in the following manner: reservoir. The platform is positioned above wave height on a base structure standing on the ocean floor or floating on the surface of the sea. The wellhead valves, which shut off the reservoir pressure, are placed on the platform, usually directly above the production wells.
The oil, which is found under high pressure in the hydrocarbon reservoir, contains large amounts of dissolved gas. The oil's capacity to retain the dissolved gas decreases with lowered pressure and rising temperature. When the oil flows up through the production well from the reservoir and past the wellhead valve on the platform, whereby the pressure decreases, gas is then given off from the oil. A mixture of oil and gas (actually a mixture of liquid (oil/water) and gas) will therefore emerge on the top side of the well head valve.
This mixture of liquid and gas is conducted to a processing plant, generally located on the platform. The function of the processing plant is primarily to separate oil and gas and to render the oil suitable for transport, and the gas suitable for transport or for return to the reservoir.
Since this process requires energy, and hydrocarbons are flammable, there must be built a number of auxiliary functions and emergency systems around the processing plant. In addition, operation of the processing and the auxiliary and emergency systems requires manpower which, in turn, requires housing accommodations and numerous other functions. For this reason, the structures become large and expensive, both in terms of investment and operation. At greater sea depths, the cost problems are aggravated when the platform and its processing plant are to stand on an expensive base structure either floating or anchored to the seabed.
Presently there are major development projects underway with the aim of reducing these costs. These include technology developed to enable placement of the wellhead valves on the ocean floor - a so-called subsea production plant. This has major economic significance because the number of platforms that are necessary to drain a hydrocarbon reservoir may thereby be reduced. A subsea production plant is situated above an area of the hydrocarbon reservoir that cannot be reached with production wells from the platform.
The production wells in a subsea production plant are drilled from floating or jack-up drilling vessels. Oil and gas from the hydrocarbon reservoir flow upward and past the wellhead valves on the ocean floor and then proceed as a two-phase flow (oil and gas in mixture) in a pipeline connecting the subsea production plant with the platform. Such a two-phase flow results in the formation of liquid slugs that produce powerful fluid knocks, uncontrolled flow conditions and a severe pressure drop within the pipeline. Therefore, the distance between the subsea production plant and the platform cannot be great. A practical limit is currently considered to be about 15 kilometers.
Technical solutions capable of increasing this distance would have major economic potential. Their most extreme consequence would be to render the platform superfluous, with the well head valves standing on the ocean floor at the hydrocarbon reservoir and the processing, auxiliary and emergency facilities being located on shore.
Work is also currently in progress on major development proj
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Britts Ramon S.
Kvaerner Rosenberg a.s. Kvaerner Kvaerner Subsea Contracting
Tsay Frank S.
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