Channel chasing in the D35 field offshore Sarawak

Abstract

The D35 oilfield was discovered in 1983 and over the next seven years, six appraisal wells were drilled to test the reservQir and hydrocarbon distribution. The productive reservoirs comprise exclusively of channel deposits of Early to Middle Miocene age, which exhibit highly variable lateral reservoir distribution. Development drilling in the field began in 1993 with fifteen wells drilled from two platforms. ' Results from this iriitial development campaign indicated that a secondary objective, the Cycle III Channel Sand was absent over much of the field. ~ resulted in a downward revision in the inplace oil volumes for this reservoir unit and downgraded its prospectivity. As part of efforts to enhance the structural and stratigraphic understanding of D35 prior to further development, a 3D survey was acquired in 1995 aimed at giving superior lateral and vertical resolution. The initial result of the interpretation appears promising. Seismic amplitude extractions at and near the Cycle III Channel Sand level have revealed features which are diagnostic of reservoir geometry and has helped explain much of the disappointing results from the first round development. More significantly the new 3D has highlighted additional scope for hydrocarbon recovery from this reservoir. DEVELOPMENT HISTORY The D35 field is located in the Balingian geological province some 130 km offshore and to the northwest of Bintulu town Sarawak (Fig. 1). The field was discovered in 1983 following which 2 appraisal wells (D35-3, D35-4) were drilled encountering the hydrocarbon accumulation in the main field area. Between 1986 and 1990 a further 3 appraisal wells (D35-5, D35-6 plus D35-6 sidetrack and D35-7) were drilled to test the northern and western limits of the field. Development drilling in D35 was undertaken from late 1993 to early 1994 and comprised of 14 wells drilled from two drilling platforms D35DP-A and D35DP-B. First oil production came on stream in October 1994.