Wells – Submerged well – Multiple wells
Reexamination Certificate
1999-06-30
2001-07-24
Bagnell, David (Department: 3673)
Wells
Submerged well
Multiple wells
C166S350000, C405S224200, C405S224300
Reexamination Certificate
active
06263971
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to systems production of multiphase petroleum effluents situated offshore at great water depths.
2. Description of the Prior Art
Many petroleum production systems are described in the prior art.
French Patent 2,665,725 describes a multiphase production system suited for reservoirs with low production capacities, that are situated in moderately deep or shallow waters. The concept of this system is based on the use of a floating structure, readily movable and provided with the necessary equipments for transferring effluents from a well to the floating structure prior to sending them to a processing or storage site. Transfer of these effluents is performed without separation of their constituents. The anchoring ties of this buoy are flexible enough to allow to displace it readily from one reservoir to another.
In patent application PCT-NO97/00,068, a submersible floating buoy is anchored above a reservoir comprising several production wells. Anchoring of this buoy is achieved by means of production risers that extend between the floating buoy and the developed area of the reservoir. Production is fed into the production risers and carried to this submersible floating structure, then sent to a processing and production plant, floating or not, such as a converted tanker, or FPSO, where it is collected and processed in order to be carried to a point of destination and of use.
Although such a system decreases manufacturing cost by saving installing equipments on the sea bottom and by using the production risers as anchors, it however has certain drawbacks. In fact, the FPSO is suitable when the developed fields have low production capacities, but it becomes less profitable in the opposite case. Furthermore, although the buoy is situated at a depth selected to minimize the effects of the sea currents and of the wave motion, the influence of these two parameters produces relative motions of the FPSO in relation to the floating structure that can lead to stresses in the line used to transfer the effluents to the FPSO. Under certain conditions, such stresses can even result in breakage of these lines.
Moreover, in the case where the pressure of the reservoirs is low, bringing the effluents up to the surface can be difficult for great water depths, or even impossible if the reservoir pressure is insufficient, and the aforementioned system is ill-suited.
SUMMARY OF THE INVENTION
The present invention is a production system and its associated implementation method, capable of producing multiphase petroleum effluents that are at a low pressure either directly at the reservoir outlet or because they are produced from reservoirs situated at great water depths.
The production system according to the invention can also be used when the pressure of the reservoir is low, for example, in the final production phase of a well.
The invention also finds applications for production of offshore petroleum effluents, oil or gas recovery.
It comprises in combination the following elements:
a) an intermediate floating station situated below the surface at a depth selected according to the pressure of the effluent at the wellhead outlet,
b) said floating station comprising one or more wellheads, each wellhead being connected to a production riser communicating with the well to be worked,
c) an anchor which anchors said floating station, said anchor being the production risers,
d) a pump situated on said floating station, said pump inporting a sufficient energy value to at least part of the effluent to ensure its transfer from said floating station to a processing or destination site,
e) an effluent transfer means, said effluent transfer extending between the floating station, the sea bottom and a final platform or a processing plant,
f) an energy source providing necessary energy for the various equipments installed on the floating station.
According to an embodiment, the pump is means one or more multiphase pumps and the effluent transfer means are, for example, one or more lines allowing to carry a multiphase effluent.
The intermediate floating station can comprise a separator which separates at least a fraction of the gas phase of the effluent and a transfer of the gaseous fraction to at least one of the wells.
The energy source can comprise a floating structure connected to the floating station by a multipurpose umbilical.
The floating station can comprise a separation device for separating at least a fraction of the gas phase of the effluent and a transfer of the gaseous fraction to a device generating electric power.
The floating station is for example situated at a depth of at least 100 m below the surface, but preferably between 150 and 300 m below the surface.
The system according to the invention can comprise several floating stations, each station being connected to at least part of an extensive reservoir (
20
) or to several reservoirs situated in a given area and supplying a common production center.
The system can also comprise one or more auxiliary pumps situated in one or more wells or in the vicinity of the sea bottom.
The production system according to the invention notably has the following advantages:
as transfer of the effluents up to the surface is no longer required, the range of workable reservoirs can be extended (possibility of producing low-pressure reservoirs),
possibility of drilling or of carrying out repair and recompletion operations from the subsurface buoy, which does not require a drilling plant provided with equipments suited for deep-water work,
the operating costs are decreased and maintenance operations are facilitated for the various equipments,
the assembly of the intermediate buoy and of the service float can be reused.
REFERENCES:
patent: 3572041 (1971-03-01), Graaf
patent: 4147221 (1979-04-01), Ilfrey et al.
patent: 4226555 (1980-10-01), Bourne, Jr. et al.
patent: 4284143 (1981-08-01), Scherrer et al.
patent: 4547163 (1985-10-01), Langpaap et al.
patent: 4762180 (1988-08-01), Wybro et al.
patent: 5007482 (1991-04-01), Forsyth et al.
patent: 5044826 (1991-09-01), Forster
patent: 5288253 (1994-02-01), Urdshals et al.
patent: 2665725 (1992-04-01), None
patent: 9734074 (1997-09-01), None
Antonelli Terry Stout & Kraus LLP
Bagnell David
Institut Francais du Pe'trole
Mayo Tara L.
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