川东北飞仙关组鲕滩天然气富集成藏特征及勘探前景

Features of gas accumulation and exploration foreground in oolitic reservoir of Feixianguan Formation in Sichuan Basin

川东北飞仙关组发现了迄今四川盆地最大的它源常压型鲕滩气田。根据天然气组分、储集层沥青以及成藏地质条件分析,天然气主要来源于古油藏原油裂解,为富含H2S的干气,H2S的形成与硫酸盐岩热化学还原作用有关。天然气的运移富集受古隆起背景的控制,分布在中三叠统雷口坡组区域性膏盐岩盖层之下,气藏形成于受断裂控制的构造圈闭中,有岩性构造型和构造型两种成藏模式,控制鲕滩气藏规模的两大关键因素是有利沉积相带内经白云岩化、溶蚀次生改造后储集性能极大改善的鲕粒岩和与构造圈闭的有效匹配,属于印支晚期—燕山期聚油气、喜马拉雅期调整定型成藏的晚期成藏类型。岩性构造型气藏包括罗家寨、渡口河及铁山坡气藏等,主要经历了印支晚期—燕山早中期的鲕粒岩聚油气、液态烃类深埋裂解以及燕山晚期—喜马拉雅期的构造形成、流体局部调整、构造控气的成藏过程;构造型气藏包括金珠坪气藏,印支晚期—燕山早中期虽有油气运移,但受储集空间所限未形成大规模液态烃类的聚集,燕山晚期—喜马拉雅期的构造形成后由构造控气。鲕滩气藏鲕粒岩分布广,资源潜力大,具有良好的勘探前景。

The biggest oolitic gas field has been found at Feixianguan Formation in northeast Sichuan Basin, which belongs to the dynamic system of other source, high press and vertical migration. The natural gas is the dry gas with high content of H2S, and mainly comes from the cracking of foregone pool. The high content of H2S in gas component is contributed to the thermochemical sulfate reduction. The gas accumulation is controlled by palaeohigh. The natural gas distributes under the territorial caprock of gypsum and salinastone at Leikoupo Formation of Middle Triassic, and accumulates in the encirclement controlled by fault. Of all pool forming conditions, encirclement and oolitic reservoir are the two major factors. The provision capability of oolitic reservoir has been greatly improved by dolomitization and corrosion of organic acid and sulfur acid. These oolitic gas reservoirs contain two kinds of forming models, namely, lithology-structure and structure. It belongs to the type of late hydrocarbon accumulation for pool forming that undergo the process of the petroleum accumulation at late Indo-Chinese epoch-Yanshan movement, and adjustment at Himalayan movement. The oolitic reservoir has a good exploration foreground due to the wide distribution and the huge resource potential.