OPTIMAL THIN OIL COLUMN MANAGEMENT—THE BREAM STORY

Abstract

Originally developed in 1987 for oil, the Bream N-1 reservoir is a Gippsland Basin Top-of-Latrobe oil and gas accumulation. The original oil column thickness varied due to local structure with most of it 13.5 m and with nearly all of it overlain by a large gas cap. The original depletion plan called for maximising oil recovery through a combination drive and included a provision for returning all produced gas to the reservoir. By 2000 this scheme had proven successful with a 60% oil recovery. The remaining life of the oil resource was, however, limited and a study of the optimum time to initiate gas withdrawals was undertaken.

Gas blow-down studies often employ full-field reservoir simulations. This stratigraphically complex reservoir is not suited to full-field modelling due to the interplay of a coning dominated thin oil column with a thinly bedded dipping reservoir. Consequently a different, more efficient tack was taken.key unswept oil areas were identified and studied for their response to a moving oil column, either through mechanistic simulations or analytically. This study with subsequent revisions concluded that gas export would increase Bream’s oil recovery by as much as 9.6 MMSTB (1.5 GL) through an active campaign of chasing the moving oil column and/or accessing it at local structural traps.

Gas export started in December 2002 after the construction of a new pipeline. Wellbore preparations were initiated in 2001 with the re-activation of previously depleted wells and the re-completion upward of existing wells. These activities have proven successful with Bream cumulative oil recovery now at 66% and oil rates higher than they have been since 1999.