Abstract

Microfossils in core samples from two wells in the Minas Field of Central Sumatra were analyzed to assist in the development of a reservoir model. Using microfaunal distributions in the modern Mahakam Delta of Kalimantan as a guide, the depositional environments of the Early Miocene (Burdingalian) Bekasap Formation (Sihaps Group) are interpreted as ranging from fluvial deltaic plain to distal delta front or possibly prodelta. Marine: nonmarine ratios of playnomorphs yield similar trends and validate using the Mahakam microfauna as a modern analog here. Biotic distributions appear to be controlled primarily by the deltaic salinity and pH gradients. The association of large coastal foraminifera with minute deeper water forms implies shoreward transport of the latter and supports the concept of a tidally dominated Bekasap delta. Future microfossil investigations may play an important role in characterizing reservoir heterogeneity as we seek to enhance our understanding of reservoir producibility.