四川盆地海相天然气富集成藏特征与勘探潜力

Gas accumulation characteristics and exploration potential of marine sediments in Sichuan Basin

四川盆地是一个高度富气的盆地，在四川盆地已发现的海相大中型气田多以孔隙型储层为主，普遍含有硫化氢（一般占天然气体积的0．2％～17％），烃类主要以原油裂解气为主。充足的气源是四川盆地海相油气富集的重要条件，古隆起为海相油气的聚集提供了圈闭条件，富含膏盐的白云岩储层为硫化氢的形成提供了硫源和催化条件。海相层系大多经历过较大的埋深，这为硫酸盐热化学还原反应的发生提供了热动力条件，而硫酸盐热化学还原反应过程更为原油裂解提供了催化条件，导致气藏中既富含硫化氢又富含甲烷气。研究表明，川东北地区飞仙关组和长兴组成藏条件优越，是最现实的勘探目的层系；四川盆地邻近膏盐层上下的大量薄层席状分布的孔隙型白云岩储层为潜在的勘探目的层；川东地区是四川盆地勘探潜力最大的地区。

Some giant gas fields recently discovered in the Lower Triassic Feixianguan Formation at the northeast part of Sichuan Basin proved that this basin is very rich in natural gas. Gas is mainly stored in the porous reservoir with high proportion of hydrogen sulfide normally being from 0.2% to 17% of the total gas volume. The hydrocarbon gas components were derived from thermal cracking of crude oil. Plenty of gas sources provided basic materials, and palaeo-uplift provided the traps for oil and gas accumulation. Gypsiferous-rich dolostone reservoir offered sulfur and catalyst conditions for the formation of hydrogen sulfide gas. The most deeply buried marine sediments provided the thermal conditions for thermochemical sulfate reduction （TSR）, which leads to the formation of hydrogen sulfide. TSR provided catalysts for oil cracking, which leads to rich methane and hydrogen sulfate in gas reservoir. The Feixianguan and Changxing formations are the most practical exploration targets due to good accumulation conditions. Potential targets exist in the thin and sheet-like porous dolostones near gypsum, particularly in the Triassic Leikoupo and Jialingjiang formations. The best exploration potential is in the east parts of Sichuan Basin.