鄂西渝东区长兴组生物礁滩天然气富集特征与勘探前景

Features of Gas Accumulation and Exploration Prospects in Organic Reef and Shoal of Changxing Formation in Western Hubei and Eastern Chongqing Region

鄂西渝东区长兴组发现了近源常压型礁滩气田,天然气主要来源于原油裂解气,具有H2S和CO2含量高的特点。天然气的运移富集受岩性-构造的控制,有构造-岩性型和岩性型两种成藏模式,控制礁滩气藏规模的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白云岩和与构造圈闭的有效匹配。构造-岩性型气藏以建南气藏为主,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;岩性型气藏以三星伴月气藏为主,储层孔隙发育和演化过程就是圈闭的发育成藏过程。礁滩气藏白云岩分布广,资源潜力大,具有良好的勘探前景。

A gas field with near sources and normal pressure was found in Changxing Formation of western Hubei and eastern Chongqing Region, where natural gas was mainly from crude cracked gas with the property of high contents of H2S and CO2 belongs to near source, normal pressure and vertical migration. According to analyzing of component of natural gas and inclusion and geologic condition forming reservoir, it was considered that the natural gas was the dry gas with high content of H2S and CO2. The gas accumulation was controlled by lithology and structure. There existed 2 hydrocarbon accumulation patterns of lithology-structure and lithology, reef gas reservoirs contain two kinds of forming models, namely, structure-lithology and lithology. The provision capability of biologic shoal and organic reef reservoir was greatly improved by dolomitization and corrosion of organic acid and sulfur acid. It belongs to the type of late hydrocarbon accumulation for pool forming that experienced the process of the hydrocarbon accumulation during the late Indo-Chinese epoch-Yanshan movement, and adjustment at Himalayan movement. The biologic shoal and organic reef reservoir has a good exploration prospects due to wide distribution and the huge resource potential.