Subsea pump system

Wells – Submerged well – Wellhead

Patent

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Details

166379, E21B 3303

Patent

active

052807665

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a subsea fluid extraction system including an electrically powered pump unit.


BACKGROUND OF THE INVENTION

In undersea fluid extraction systems, operational efficiency can be improved by the use of submersible pumps, in particular where production is from wells remote from a mother platform or fluid processing facility, so that the well effluent requires to be transported over substantial distances. Submersible pumps could also be used in multi-phase marginal field wells where the fluid is monophasic downhole. However electrically powered submersible pumps tend to be very prone to breakdown and are generally unreliable. Average operational times before failure may be only a few months. More often than not, failure is due to a damaged external power cable. Such pumps are accordingly unattractive economically because of the cost of frequent well shut-downs.
The present invention is concerned accordingly with the provision of a submersible pump system for subsea use which avoids the above-mentioned disadvantage.


SUMMARY OF THE INVENTION

The invention thus provides a subsea pump system in which an electrically powered pump unit can be run and retrieved by means of a relatively rigid, for example, pipe-like, conductor assembly by which the pump unit is energized in use.
The invention also provides, in wellhead structures for a subsea fluid extraction system, an X-mas tree which mounts an electrical conductor assembly carrying at least one electrically powered pump unit in a manner permitting running and retrieval of the pump unit through the X-mas tree.
The conductor assembly is conveniently constituted as a tubular assembly comprising concentric tubular conductors. Barrier or dielectric fluid supply or circulation is advantageously associated with the conductor assembly and appropriate piping can be included for this purpose.
The X-mas tree of the invention thus can comprise a hollow stem having at its upper end, which is normally closed by a protective cap, a hanger for the conductor assembly or power tubing. Production tubing extends downhole from the wellhead structure and the conductor assembly is suspended from the hanger so as to extend within it to define a space between the tubing and the assembly for the well effluent. Valving for the pumped effluent is carried by an X-mas tree block below the hanger.
The mounting of the conductor assembly or power tubing in the X-mas tree permits the pump unit to be run and retrieved on the rigid power tubing in a manner similar to a wire line operation, that is, the power tubing or assembly is run through the X-mas tree. In appropriate circumstances, the pump system can be run and pulled without killing the well.
The electrical conductor assembly can be suitably configured in accordance with the disclosures of EP 0 063 444 (FD1/2), and EP 0 089 121 (FE3), with conductor tubing surrounded by outer piping to constitute power tubing in which a barrier fluid can be circulated between the wellhead and downhole equipment. The conductor assembly can thus conveniently comprise a plurality of concentric tubular conductors, typically three for a 3-phase power supply, separated by solid insulation. External insulation for the tubular conductors can be effected similarly and/or by dielectric fluid, typically an insulating oil which may be circulated within and outside the conductor tubing by means of spaced outer tubing within which the conductor tubing is received.
The system of the invention thus includes no electric cabling susceptible to damage during running and pulling operations so the mean time before failure is expected to be substantially increased as compared with prior art systems, perhaps to two or three years, with evident economic advantage. Moreover, cable handling and feed-through equipment is rendered unnecessary.
A contribution to improved reliability is obtained by adoption of a barrier fluid system. Thus, a barrier fluid circulated by means of the power tubing can be employed for cooling lubrication and

REFERENCES:
patent: 3347311 (1967-10-01), Word, Jr.
patent: 3437149 (1969-04-01), Cugini et al.
patent: 3638732 (1972-02-01), Huntsinger et al.
patent: 4154302 (1979-05-01), Cugini
patent: 4331203 (1982-05-01), Kiefer
patent: 4363168 (1982-12-01), Bryer et al.
patent: 4391330 (1983-07-01), Kiefer
patent: 4462464 (1984-07-01), Brown et al.
patent: 4804045 (1989-02-01), Reed

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