八角场地区香四段气藏的成因与意义

Genesis and significance of Xiangxi 4 gas reservoir of Upper Triassic in Bajiaochang Area

四川盆地中部八角场地区香四段气藏得以成藏的关键是有利储层的发育和压力封闭。在低A/S条件下发育的砂体,有较高的孔隙度和渗透率,是优质的储层,而在较高A/S条件下发育的砂体,其物性较差,是不利的储层;八角场地区香四段气藏位于上三叠统异常压力封闭系统内,香四气藏内部异常高的地层压力主要是构造挤压和烃类生成作用形成的,在这种超压条件下的水溶相天然气的脱溶作用是成藏的重要因素。

Gas accumulation depends on not only the reservoirs with higher porosity and permeability but also pressure sealing in the Xiangxi 4 gas reservoir, Bajiaochang Gas Field. The sandstones developed under lower A/S conditions have higher porosity and permeability. The sandstones formed under higher A/S conditions are poor reservoirs because of reduced permeability and porosity. Xiangxi 4 gas reservoir is distributed in Upper Triassic （T3） overpressure system. The overpressure is caused by tectonic compression and the hydrocarbon formation. The key factor of gas accumulation is degasification of the water-soluble gas under overpressure conditions.