Pyrite, as one of the important components of shale, is of very important impact on shale gas enrichment. However, there are few researches on it presently. Therefore, based on outcrops, drilling cores, thin sections and test data, characteristics of pyrite in organic-rich shale section of the Longmaxi Formation and its impact on shale gas enrichment was studied in this paper. The result shows that pyrite occurred in different forms (macro-micro scale) in the Longmaxi Formation in the Southeast Sichuan Basin. The formation and content of pyrite has a close relation with TOC content. Pyrite may catalyze the hydrocarbon generation of organic matter. Interparticle pores within the pyrite framboids and organic matter pores in the pyrite-organic matter complex are well developed in the Longmaxi shale, which provide reservoir space for shale gas. Pyrite can promote the shale gas enrichment by absorbing shale gas on its surface and reserving free gas in the interparticle pores and organic matter pores. In addition, as a kind of brittle mineral, pyrite can improve the brittleness of shale reservoir and increase the micro-nano pore system in shale reservoir, improve the transmission performance of shale reservoir and boost the shale gas recovery.



This study was supported by the National Natural Science Foundation of China (NSFC) (41602147, 41702149, 41728004). We wish to thank SINOPEC for providing the samples and some test data for this study.



Keyword: Shale reservoir; Pyrite; Longmaxi Formation; Southeast Sichuan Basin





黄铁矿对页岩气富集的影响——以川东南龙马溪组为例



黄铁矿作为页岩的重要组分之一,其对页岩气的富集具有重要影响作用,但目前针对页岩中黄铁矿的研究较少。因此本文选取川东南龙马溪组海相页岩为研究对象,基于露头、岩心、薄片和分析化验资料,对龙马溪组优质页岩层段中黄铁矿的特发育特征及其对页岩气富集的影响进行研究。结果表明:川东南龙马溪组黄铁矿发育形态类型多样（宏观-微观尺度）。黄铁矿含量与 TOC、气态烃(S2)含量之间具有较好的正相关性和S1(岩石中残留烃含量)呈反比,反映了黄铁矿的形成和含量与有机质含量之间存在密切关系,并可能对有机质生烃起到催化作用。研究区龙马溪组页岩内黄铁矿晶间孔、黄铁矿与有机质复合体中有机孔发育, 这些孔隙可以作为页岩气的储集空间。另外黄铁矿含量与甲烷吸附气量具有明显的正相关性,通过对黄铁矿表面进行能谱分析发现,黄铁矿表面聚集了大量烃类物质,因此黄铁矿可以从吸附和聚集游离气两个方面促进龙马溪组页岩气的富集。另外黄铁矿作为一种脆性矿物,可以提高页岩储层的脆性以及页岩储层在后期酸-氧复合压裂液作用下,黄铁矿会被溶蚀、氧化消耗并释放热量,产生诱导孔-缝,进而增加储层微-纳米级孔隙系统,改善页岩储层传输性能、提高页岩气的采收率。



关键词：页岩储层；黄铁矿；龙马溪组；川东南