Petroleum generation, migration, and entrapment in the Zhu 1 depression, Pearl River Mouth basin, South China Sea

Analysis of crude oils from several fields in and near the Huizhou sag, Zhu 1 depression, Pearl River Mouth basin, provides an excellent demonstration of inferring petroleum generation, migration, and entrapment in areas where drilling encounters hydrocarbons but fails to penetrate the effective generative sequence. This paper illustrates the integration of geochemical, geophysical, and geological interpretations to develop a model of petroleum generation, migration, and entrapment. The Zhu I depression is one of three subbasins in the Pearl River Mouth basin. Sediment fill within the subbasin consists of Paleogene synrift units and Miocene to Recent postrift deposits. Although drilling in the Zhu 1's Huizhou sag and on the adjacent Dongsha Massif has netted numerous oil discoveries since the early 1980's, it has not encountered any effective or potential source rocks within the penetrated sections. However, interpretation of the systematic variations in crude oil chemistry within the regional geologic and structural framework has been invaluable in inferring source attributes and delineating location and distribution of the unpenetrated probable source. The signatures resulting from genetic and alteration processes suggest that high-wax oils were generated in mature, lacustrine source facies of the synrift sequence and were expelled into a tightly sealed massive sandstone carrier system. They migrated south-southeast toward the Dongsha Massif, were entrapped to spill point in traps along the migration route, and were altered increasingly within the successively shallower and cooler reservoirs on the massif. (C) 1998 Elsevier Science B.V. All rights reserved.