Wells – Submerged well – Means removably connected to permanent well structure
Patent
1999-05-20
2000-10-10
Dang, Hoang
Wells
Submerged well
Means removably connected to permanent well structure
166372, E21B 4336
Patent
active
061291501
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and equipment to encourage the flow, to the surface, of hydrocarbon mixtures containing a high concentration of gas. It may be applied in a single offshore oil well or in an undersea gathering line (manifold) which receives the production from various wells for subsequent delivery.
In the flow of oil, as occurs in undersea production lines, large pressure head losses occur, due mainly to the high flow rates of gas and oil which flow simultaneously and which give rise to high shear stresses in the flow.
In the technique of deep offshore production another factor giving rise to high pressure gradients is the great difference in level between the wellhead and the platform, which frequently makes it necessary to use long vertical pipes, known to those skilled in the art as "risers", to deliver the production flow to the surface.
These factors result in there being high pressures at the wellhead or in the undersea gathering line (manifold), significantly reducing production.
This invention aims to promote primary separation of the liquid and gas phases of the fluids produced by an oil producing well and to encourage flow of these two phases to a gathering centre along separate flow lines.
Accordingly one aspect of the present invention provides equipment for offshore oil production for the intermittent injection of gas, characterized in that it comprises:
a subsea primary separating means which receives the production from an offshore oil well leaving a wellhead via a flow line;
a separated gas flow line which connects the top of the primary separating means to a collecting vessel located at a gathering centre; a flow line which is fitted with a check valve, which connects the lower part of subsea primary separating means to a U-shaped length of pipe which has one of its ends connected to a flow line and its other end connected to a surge tank located at the or a gathering centre;
shut-off valves in the respective flow lines close to the surge tank;
a high pressure gas injection line which connects compressed gas supply system to a said flow line at a point close to the surge tank;
a high pressure gas injection line which similarly connects the gas compressed gas supply system to the other said flow line; and
high pressure gas injection lines fitted with respective shut-off valves.
The undersea primary separating means receives the fluids produced by the oil well and brings about a primary separation between the liquid and gas phases.
The gas phase flows to the gathering centre along a line connected to the top of a separating vessel serving as the undersea primary separating means.
The liquid phase flows to the gathering centre along a flow line which distributes the fluids into the U-shaped length of pipe, each end of which is connected to flow lines.
High pressure gas injection lines connect a compressed gas supply system to the flow lines and make it possible to inject high pressure gas into each of these flow lines for a specific period so as to assist removal of the liquid phase accumulating in these lines. The shut-off valves located in the high pressure gas injection lines are used to enable the flow of injected gas.
The check valve fitted in the flow line which distributes fluids to the U-shaped length of pipe prevents the high pressure gas injected into the flow lines from passing into the undersea primary separating means.
If it is desired to increase flow efficiency, a mechanical interface can be used to push the liquid phase deposited in the flow line to the gathering centre. In this case the high pressure gas injection lines must be provided with means to allow a mechanical interface to be inserted into the flow lines. The flow lines must also be provided with means which make it possible to remove the mechanical interfaces, if necessary without interrupting production.
The separated gas flow line may be fitted with a pressure control valve which provides control of the level of the liquid phase of fluid produced which accumulates in the undersea primary separati
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Dang Hoang
Petroleo Brasileiro S.A. - Petrobras
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