Subsurface Facies Analysis and Reservoir Characterization of the Late Oligocene Penyu Formation, Shallow Marginal Marine to Low Energy Deltaics Sediments, Penyu Basin, South China Sea, Malaysia

The subsurface facies analysis was based on a single well penetrating the Late Oligocene K1 – K10 sands of the Penyu Formation in the Eastern reaches of the Penyu Basin. This well acquired an extensive data suite including; conventional wireline (gamma-ray, lateralog resistivity, density-neutron, acoustic), specialized data such as electrical imaging, nuclear magnetic resonance, elemental capture spectroscopy and dielectric propogation. In addition, the entire reservoir succession was conventionally cored and drill-stem tested. The borehole conditions were good and therefore the data quality was excellent for detailed facies analysis. The image log was calibrated to core, and detailed facies analysis was extended beyond the core using the geological features from the images, the porosity and permeability from conventional density-neutron and the nuclear magnetic tool and the mineralogy from the elemental capture spectroscopy.Three major lithological groups were identified sandstone, heterolithic and mudstone with each facies often transitional to the next. The overall depositional environment has been interpreted as restricted shallow marginal marine bay adjacent or proximal to a low energy delta or estuarine mouth.