DEVELOPMENT AND EVOLUTION OF MUD DIAPIR AND MIGRATION AND ACCUMULATION OF NATURAL GAS AND CO₂ IN YINGGEHAI BASIN

Because mud diapir is a geologic and seismic abnormal body with low density and velocity and high temperature and pressure in Yinggehai basin in the western margin of the South China Sea, its evolution and associated upwelling of heat flow are closely related to migration and accumulation of natural gas and CO₂. Regionally,geothermal field and geothermal flow values are the highest in the diapiric structural zone in the middle of the Yinggehai basin,and become decreased towards the sides of the basin(non-diapiric areas). Yinggehai diapirs have obvious geologic-geophysical characteristics of low density, low velocity, high temperature and high pressure,and can be grouped under"deeply buried"low amplitude of weak-intermediate energy, " shallowly buried"high amplitude of intermediate-strong energy, and "vent"-typed high amplitude of extremely high energy. Natural gas migration and accumulation in the Yinggehai basin have characteristics of young hydrocarbon source rocks,dynamic equilibrium pooling in late times, and diapiric upwelling flows controlling activities of natural gas and CO₂. Shallow natural gas and CO₂ migrate and accumulate in blocky and stratified way,and blocks and strata influenced by diapiric upwelling flows can see CO₂ sources formed locally, resulting in the complexity of CO₂ sources. CO₂, gas is mainly dis shallow diapiric areas of high geothermal field,and hydrocarbon gases are concentrated in other areas.