Two developments the latter part of last year advanced the field-use history for multiphase technologies.
Three multiphase pumps were commissioned in Europe and offshore Malaysia. And field trials of a three-phase subsea flow meter were begun in the North Sea.
PUMP COMMISSIONINGS
An MP40 pump, manufactured by Multiphase Systems Plc, Bristol, U.K., and installed on the Boker B platform, offshore Lutong, Sarawak, Malaysia, was commissioned on Aug. 31, 1989.
The unit is one of a line of pumps from Multiphase Systems that incorporates twin parallel shafts, geared to counter-rotate and carry pumping elements which intermesh, to give a constant volume axial displacement of fluid from each towards a central delivery branch (OGJ, Feb. 6, 1989, p. 51).
During the commissioning trials, the MP40 pump on Boker B handled gross inlet volumes of 95,000 b/d at differential pressures up to 370 psi, says Multiphase Systems. The differential pressure was limited by the power availability from the gas engine provided by the customer.
The gas-volume fraction exceeded 97% without recirculation at inlet pressures down to 25 psi.
The pump began a 12-month endurance run on Sept. 5. It is handling 75,000 b/d gross inlet volume at 150 psi differential pressure with a gas-volume fraction of 9294%.
Commingled fluids are being taken from 4 to 6 wells through a manifold directly into the pump. The inlet pressure has been set at 70 psi which is 5060 psi below normal flow conditions.
The resulting incremental oil is being monitored.
Elsewhere, an MP10 pump from Multiphase was installed on a land well in Europe and successfully commissioned on Oct. 12, 1989 (Fig. 1). The pump is handling 6,000 b/d at a very high differential pressure of up to 40 bar.
Commingled fluids are being taken direct from this well head with an inlet pressure at 9 bar and a gas-volume fraction of 85-90%.
The MP10's endurance test is scheduled to run for an initial period of 6 months.
Another MP40 pump was installed on Forties Bravo platform in April of last year and preliminary commissioning carried out in May 1989.
Shortly after installation, however, widespread industrial unrest among employees of contractors across the North Sea disrupted the work program on Bravo.
On Oct. 19, 1989, offshore commissioning was announced to recommence during the first quarter of 1990. The commissioning period was anticipated to last 4-5 weeks.
FLOWMETER INSTALLED
Texaco Exploration & Production Technical Division took delivery late last year of a 6-in., three-phase flowmeter manufactured by Gervase Instruments Ltd., U.K. Field trials at Texaco U.K.'s Tartan platform began at the end of August 1989. Following these trials, the meter is to be installed in 160-m water at Texaco's Highlander template.
Specified standards for the meter included high pressure (2500 ANSI), special materials, and tight accuracy requirements.
The body and flanges are of duplex stainless schedule 80, selected for its high tensile strength/low weight ratio and high corrosion resistance, according to Gervase. All internals are 304 and 316 austenitic stainless except the spring which is inconel 75OX (Fig. 2).
Texaco's venture into three-phase flow metering in offshore oil exploration has resulted in development of a flow rig capable ultimately of carrying out analysis of gas, oil, and water on the sea bed.
This will eliminate the need for test lines to a host platform.
In the case of Texaco's Highlander field, the well head is 8 miles from the platform. A conventional separate test facility with a subsea slug catcher, riser, and dedicated test separator represented between 15 and 20% of the total development costs of $100 million (OGJ, Nov. 11, 1985, p. 58; May 5, 1986, p. 112).
The Texaco three-phase metering system can be either positioned subsea away from the host platform or, in cases of fields producing directly to shore, the system can be located on shore, says Gervase.
The system separates most of the gas from the product by an inclined plate separator, and the gas volume and mass are metered by a vortex meter. The total product is remixed (water, oil, crude, and some gas) and metered volumetrically by the Gervase Gilflo primary flow sensor.
A mass computation is made incorporating pressure, temperature, and density correction. From this can be calculated the residual gas absorption in the three-phase product.
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