莺歌海盆地泥底辟发育演化与天然气及CO2运聚成藏规律

泥底辟是南海北部边缘西区莺歌海盆地颇具特色的地震地质异常体,具有低密、低速及高温高压特征,其发育演化及所伴生的热流体上侵活动与天然气及CO2运聚分布乃至富集成藏均密切相关。将莺歌海盆地泥底辟划分为"深埋型"(低幅度弱-中能量泥底辟)、"浅埋型"(高幅度中-强能量泥底辟)及"喷口型"(高幅度特强能量泥底辟)三大类进行研究。研究表明,晚期泥底辟及热流体活动不仅为浅层天然气及CO2运聚戍藏提供了纵向的高速运移通道和运聚动力条件,促使深部天然气及CO2向浅层大量运移聚集,而且导致盆地具有烃源岩早熟、天然气运聚供大于散的晚期动平衡戍藏,以及泥底辟热流体上侵活动控制天然气及CO2运聚规律之特点。

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 distributed in shallow diapiric areas of high geothermal field,and hydrocarbon gases are concentrated in other areas.