川西坳陷中段侏罗系气藏特征与富集主控因素

Characteristics and main factors controlling the Jurassic gas reservoirs in the middle section of the Western Sichuan Depression

川西坳陷中段侏罗系发育大面积低丰度岩性、构造—岩性气藏。气藏普遍具有多层叠置、局部富集高产、无明显气水边界、低温、超压的特征。结合各构造单元侏罗系具体成藏条件研究认为,侏罗系整体为"下生上储"式成藏组合,天然气主要来源于下伏须家河组四、五段烃源岩。因此,具备良好的沟通源、储层垂向运移输导体系是天然气富集成藏的关键因素。侏罗系各组段砂岩储层物性纵、横向变化较大,受渗透率级差影响,相对优质储层的发育程度是天然气藏高产富集的主要控制因素。龙门山前及龙泉山两侧发育大量直通地表的断裂,不仅直接破坏了断裂带附近的盖层条件,同时破坏了与之相接的斜坡区侏罗系砂体上倾方向的封闭性,有效的圈闭是侏罗系富集高产的重要因素。

In the middle section of the Western Sichuan Depression,lithologic and tectonic-lithologic gas reservoirs are widespread in the Jurassic. These reservoirs feature multiple layers,local enrichment,no obvious gas /water boundary,low temperature and overpressure. Accumulation conditions in the Jurassic indicate that gases were mainly sourced from the Lower Jurassic and preserved in the Upper Jurassic. The fourth and fifth members of the Xujiahe Formation provided important source rocks for natural gases. Vertical pathways connections between source rocks and reservoirs were the factors controlling natural gas accumulations. The physical properties of the Jurassic sandstones varied both horizontally and vertically. The development of favorable reservoirs also influenced the enrichment of natural gases. A large amount of vertical fractures which extended directly to the earth surface were found in the front of the Longmen Mountain and on both sides of the Longquan Mountain. They destroyed the neighboring cap formations,and damaged the sealing capacity of the Jurassic sand bodies in the adjacent slope area. Effective traps were necessary for natural gas enrichment in Jurassic.