Under waterflood development, gas production from the Brent Field will fall off plateau in 1998 and, at field abandonment, it is estimated that approximately 55% of the 6.9 Tscf GIIP and 54% of the 3600 MMstb STOIIP would be recovered.

With its high solution gas-oil-ratio, reservoir depressurisation, as an enhanced recovery project, is an attractive possibility. In this process, reservoir pressures would be progressively lowered, ultimately to approximately 1000 psi.

It is expected that gas liberated from residual and by-passed oil would increase gas recovery by over 1 Tscf allowing the field to continue to produce at plateau levels into the 21st Century. Depressurisation is also expected to increase oil and condensate recovery by 30 MMstb compared to a continuation of the ongoing waterflood. From a sub-surface viewpoint, the main challenge would be to manage the field to maximise oil recovery while maintaining gas sales at plateau.

To allow the field to move into a new development phase, an extensive platform modification programme will need to be initiated. Planning has to take into account the uncertainties associated with a project that has not been tried on an oil reservoir of such a scale. Aquifer influx, H2S and sand production are some of the risks that have been assessed and contingency measures identified.

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