The sihapas Group has significant oil accumulations in the Pematang and Bekasap fields, Central Sumatra. The Sihapas sandstone reservoir is light gray to brownish gray, fine to coarse grain in size, some granules, silty, friable, calcareous, and glauconitic, with traces of mica and a carbon clay matrix. Carbonaceous material and macro fossils are common in the shale. The Lower Sihapas reservoirs were deposited in a shallow marine to deltaic system environ-ment associated with a distributary channel. It gradually changed from a deltaic , shallow marine to an open marine environment during the deposition of the Upper Sihapas Group (Bekasap and Duri Formations). The Sihapas deltaic sequence creates a unique pattern of porosity distribution will be discussed and correlation among the three will be defined. It can be shown that a unique pattern can be established from this study so that future identification can be made in a similar deltaic sequence elsewhere. This study is part of PT Caltex Pacific Indonesia’s effort to increase its production output through enhanced oil recovery projects in which detailed heterogeneity analysis is critical to define the best geologic model.
Authors : Untung Suryanto & Nirwan Said