Abstract
Under the current waterflood development, it has been predicted that gas production from the Brent Field will fall off plateau in 1998 and, at field abandonment approximately 55% of the 6.9 Tscf GIIP and 54% of the 3600 MMstb STOMP would be recovered.
A review of EOR/IOR techniques was carried out at an early stage to define which of the various processes might be applicable in the Brent Field and would warrant further evaluation. The scouting study considered microbial, thermal, chemical, gravity drainage and miscible processes as well as reservoir depressurisation.
Of all the possibilities, surfactant flooding, immiscible (or near miscible) gas Injection and depressurisation were found to be technically viable. However, based on an estimate of the costs involved it was established that only reservoir depressurisation was economically attractive under the current and projected oil price trend.
With its high solution gas-oll-ratio (ranging from 1500 to 3000 scf/stb), depressurisation of the field, ultimately to 1000 psi, would liberate a significant proportion of the remaining solution gas and raise recovery by 1.5 Tscf. It was also established that, by extending the field's life, oil and condensate recovery would be Increased by 30 MMstb compared to a continuation of the ongoing waterflood.
Before the project could be initiated uncertainties such as aquifer influx, reservoir souring, compaction, subsidence and sand production had to be assessed and contingency measures identified. In addition, the full range of engineering options for the four platforms had to be costed and evaluated. With a planned expenditure of £1.3 Billion, the Brent Field will be able to sustain oil and gas sales well into the next century.
