莺歌海盆地底辟构造带天然气运聚特征

底辟构造带是强超压发育区 ,也是莺歌海盆地超压源所在地 ,属典型的垂向超压传递压力系统 ,热流体活动十分活跃 ,具独特的天然气垂向运移特征。研究表明 :(1)异常温压形成强流体势 ,异常高压为天然气运移提供强大动力 ;(2 )流体压裂形成良好的天然气垂向运移输导系统 ,底辟带热流体输导系统主要是流体压裂面 ;(3)热流体活动模式决定了天然气运移 ,流体压裂可导致流体释放 ,使孔隙压力降低 ,并造成流体压裂面自动封闭 ,尔后地层压力再次聚集增大 ,再次导致流体压裂和流体释放 ,依此反复 ,形成流体幕式活动。天然气作为热流体的组成部分 ,其成藏特征为幕式聚集和处于聚集散失再聚集供大于散的动态平衡中

MIGRATION-ACCUMULATION CHARACTERISICS OF NATURAL GAS IN THE DIAPIR STRUCEURE BELT OF YINGGEHAI BASIN

The diapir structure belt is the highly overpressured zone and the overpressure origin of Yinggehai basin. It belongs to a typical vertical pressure\|transfer system. The hot fluids were very active in this zone. The gas migration and accumulation showed three very different features from other hydrocarbon\|bearing provinces. First, the abnormal temperatures and pressures produced high fluid trend, and the abnormal pressures provided a great force to gas migration. Second, hydrofracture generated a good vertical migration path for natural gas, and the fluid\|transporting system in the diapir structure belt is mainly the fractured surface. Third, the activity model of the hot fluid controlled gas migration. Hydrofracture caused the release of fluid, which lowered the porosity pressure. The fractured surface was resealed after the release of fluid. The formation pressure increased again with the thickening of the overburden rocks, which caused the release of fluid again. This process repeated and the shutter\|like activity of fluid formed. As a part of the hot fluid, the accumulation of the natural gas is shutter\|like, and the gas is under the positive dynamic balance of accumulation\|dissipation\|reaccumulation, in which the supply of gas is greater than its dissipation.