Subsea Processing System Ready for Gulf of Mexico Field

Abstract

ABSTRACT: Use of subsea processing (i.e. subsea separation and Single phase pumping) to produce smaller more remote oil fields has been the subject of field tests and studies since 1969, reported in 9 OTC papers from 1974-1992. The advance in GLASS [a] is to create a relatively "low tech" and proven solution. Although originally intended for the Gulf of Mexico, it may be applicable in Brasilian, North Sea and other areas. Parallel with the engineering development, composite judgments have been developed for the economic performance for CAPEX and OPEX using recently available probabilistic methods. Connector advances in 1991–1992 may further simplify use of this system design. Application is relatively insensitive to water depths, e.g. 300–3,000fi. Offset distances from a host platform may be in the region of 5–50 miles. The system was developed for a Base Case in l,500ft. of water with 12,000 bopd initial production with 8 wells from a 25 MMBBL recoverable reservoir, with GORS in the region of 1,000 scf/bbl. Installation equipment comprises the semisubmersible drilling unit and standard offshore service vessels, implying economy and flexibility for use in worldwide application. Hydrate, sand, shutdown and startup operating conditions were addressed. PRECEDENT SINCE 1969: The first trials for a subsea processing system were the experiments in 1969-1971 offshore Abu Dhabi at the Zakum field, conducted by BP and Total when they installed a subsea separator and booster pump in about 72 feet of water and operated the system over a three year period, including a year long period when about 1.7 MMBBL of oil was produced. OTC paper no. 1942 in 1974 outlined this pioneering effort. That prior work was systemized and updated for North Sea field conditions in the GA-SP project (e.g. 30,000 bopd from 4 wells in 984 fl. of water), culminating in full scale prototype trials in a dry doc kin 1990on behalf of eight operators: it was reported in OTC papers 6722, 6766 and 6767 in 1991. This system design used water injection hydraulic power to drive the booster pump, a 4 level component arrangement and a multiple stage subsea separator to provide oil of export quality from a hypothetical arrangement of 4 producing wells with 4 water injection wells, with GORS of about 450. Another series of experiments with a subsea separator was made in live offshore conditions in about 248 ft. of water, near the base of a platform in the North Sea operated by Hamilton Brothers. This test series with the BOET separator design is reported in OTC paper nos. 5922 and 6423 in 1989 and 1990, respectively. It would therefore appear that significant precedent now exists for subsea processing - indicating it is concept whose time has arrived. ENHANCED RECOVERY FROM REDUCTION IN WELL BACK PRESSURE: A major benefit of the use of subsea separation and boosting in deep water is that the back pressure on the wells can be reduced and total recovery can be enhanced.