NUMERICAL SIMULATION OF THE OVERPRESSURE IN THE DEEP-WATER AREA OF THE PEARL RIVER MOUTH BASIN, NORTHERN SOUTH CHINA SEA: A CASE FROM SITE 1148, ODP LEG 184

The present porosity and overpressure in the deep-water area of the Pearl River Mouth Basin (PRMB) have been calculated with the logging and core data of site 1148, ODP184, on the northern slope of the South China Sea, and the evolution of porosity and overpressure in the 30Ma is simulated with the hydrodynamic model, which has been applied to investigate the characteristics, evolution and controlling factors of the overpressure. The study shows that the Pleistocene shallower than 100 m display normal formation pressure, and overpressure only occurs in the deeper strata. Porosity and pressure increase as effective stress decreases at about 460 m depth, corresponding to the presence of the slumped unit. The evolution of the early-deposited sediments did not fully agree with the present field. The overpressure during 28.5 to 23.8 Ma decreased sharply, which could be the response to the erosion event during this period on the northern slope of the South China Sea. Deposition rate is the dominating factor to the evolution of formation pressure in the deep-water area of PRMB. This study would be of theoretical and practical importance to the hydrocarbon-bearing basin with overpressure.