南盘江盆地茅口组生物礁碳酸盐岩成岩特征

The Diagenetic Characteristics of Reef Carbonate of the Maokou Formation in the Nanpanjiang Basin

生物礁油气藏是油气勘探的一个重要目标,其储集性能的好坏是控制它能否成藏的关键。中二叠世南盘江盆地发育以海绵类为主要骨架的生物礁,其经历了海底潜流、淡水、埋藏、表生等成岩环境,最后抬升出露地表遭受侵蚀。所发生的成岩作用主要有:胶结、溶蚀、白云化、硅化以及压实、压溶作用。在前两种环境中,主要是胶结作用,伴随溶蚀,这一阶段储层孔隙性遭到了一定程度的破坏;浅埋藏阶段的胶结最终填满孔隙;而中-深埋藏环境下的有机流体充注溶蚀以及相应发生的白云岩化作用有效改造了储层的孔隙性,该区处于埋藏条件下的台缘生物礁是有利的油气勘探目标。

The reef oil-gas pools are an important target in the oil and gas exploration. Its reservoir quality is of great importance. Generally, the main controlling factors of development of reef reservoir include deposition, structure and diagenesis. The former two have influence over the distribution of the reservoir and the latter determines the quality. In the Middle Permian, reef constructed mainly by sponges was well developed in the Nanpanjiang basin. This article deals with controls of diagenesis over reef reservoir conditions in the Nanpaniiang basin based on thin section observation. The study indicates that the reef experienced the submarine phreatic, freshwater, buried, epigenetic environments in turn and uplifted to the surface to be eroded at last. The diagenesis happened in those conditions includes cementation, dissolution, dolomitization, compaction and pressure solution. The cementation primarily occurred in the submarine phreatic and freshwater environments and accompanied by dissolution with reservoir porosity destroyed to some extent. Going into the shallow buried environment, pore space in the reef was almost filled with cements. Sanking to the middle-deep buried environment, dolomitization and dissolution took place in the reef, which improved reservoir porosity significantly. So the reef under buried environment will be a favorable exploration target.