Petrophysical interpretations of subsurface stratigraphic correlations, Baram Delta, Sarawak, Malaysia

Abstract

Petrophysical well log data help to predict hydrocarbon reserves before field development which involves huge financial commitment. In this study, reservoir characterization was performed with a view to obtain information on the geological formation type and petrophysical parameters. Wireline log data obtained from five wells were used to develop a 3D model of X-field in the Baram Delta which was in turn evaluated using the PETREL software. Suites of gamma ray, sonic, density, resistivity and neutron logs aided the delineation and correlation of the sandstone formation. Fourteen hydrocarbon-bearing sands were defined from well log data and divided into two-reservoir zones, shallow and deep. Well correlation assisted in the delineation of the reservoir sands across the wells. The quality of the reservoir formation was evaluated from average petrophysical properties: with an average thickness of 62 m, an average porosity of 0.19, an average net-to-gross ratio of 0.068, an average V-shale of 0.45, and an average water saturation of 0.95. A rollover anticline structure was identified across the field using the fault as a description tool. Variation of petrophysical parameters and uncertainty in the reservoir properties were included to predict the effect on the volume of oil in place. This study revealed that the discovered hydrocarbon reserve resource accumulations in the Field X for the fourteen-mapped reservoir sands have a total proven reserve resource estimate of 740MMSTB at P90, 655MMSTB at P50 and 593MMSTB at P10. Reservoirs A and B are the only intervals with the highest recoverable oil, a volume of 256MMSTB at P90, 215MMSTB at P50 and 181MMSTB at P10, respectively. These analyses facilitated an improved reservoir description of shaly sandstone, which contributes to better planning of hydrocarbon re-development and future recovery, and thereby improving the energy supply security of the regions.