Modelling of Pressure Evolution and Hydrocarbon Migration in the Baiyun Depression, Pearl River Mouth Basin, China

The Pearl River Mouth basin is one of the most important offshore basins in China. Petroleum exploration is being carried out in the deep water area of the basin. Well tests indicate that the pore pressure is normal in the shallow water area. The hydrocarbon migration and geopressure distribution in the deep water area are poorly understood at present. These issues have been considered using geological data and basin modelling. The modeled results indicate that pressure accumulation and release, and fluids migration have a close relationship with structural movement. On the basis of our investigation, the following conclusions have been drawn: (1) At least three episodic accumulations and release of pressure occurred in the Cenozoic. The pressure release and associated hydrocarbon migration occurred primarily during the Dongsha Movement, when most of the overpressure was released to normal pore pressure except for some overpressure in the deep water area. (2) Both the measured pressure and the modeling results indicate that pressure is normal in the shallow water area and is abnormally high in the deep water area at present stratigraphy. Difference of pressure distribution is caused by lithologies and facies, because of the high percentage of mudstone deposited in the deep water and the high percentage of sandstone in shallow water. (3) The hydrocarbon migrated to the shallow and deep water areas along faults. Because of the high ratio of sandstone in the shallow water and high ratio of mudstone in the deep water area, the hydrocarbon scattered into the sandstone more easily in the shallow water area, so large oil & gas fields appear to form more easily in the deep water area.