CHARACTERISTICS OF MUD DIAPIR AND GAS CHIMNEY AND THEIR RELATIONSHIP WITH RESERVOIR FORMING FOR PETROLEUM AND NATURAL GAS HYDRATE ON NORTHERN SLOPE OF THE SOUTH CHINA SEA

Based on the geological and seismic data collected from the deep water area, mud diapirs and gas chimneys are recognized in the Qiongdongnan Basin and Baiyun sag of the Pearl River Mouth Basin on the north slope of the South China Sea. Also discussed are the distribution pattern, evolutionary history, genetic features and their relationship with the accumulation of petroleum and natural gas hydrate. It is found that: (1) mud diapirs and gas chimneys are mainly distributed in the central part of a sag or the transition zone between sag and uplift and characterized by muzzy or chaotic seismic reflections. The dimension of the mud diapir and gas chimney varies and the strata penetrated by them are also different. Vigorous hot fluid flow activities may occur.(2) the evolution and development of mud diapir and gas chimneys are controlled by the thick shale deposited in the depressions, high temperature and overpressure, weak structures such as faults and micro-cracks, and pressure enhancement during the process of hydrocarbon generation. (3) mud diapirs and gas chimneys as well as associated structures are favorable pathways for deep hydrocarbons migrating from the deep to shallow. The gas-bearing fluid would finally migrate through those conduction systems to Neocene reservoirs and natural gas hydrate stability zones, and formed a vertical sequence with oil and gas pool below and/or natural gas hydrate on top.