四川盆地五峰组—龙马溪组笔石与页岩气关系探讨

前人对笔石的研究主要用于地层划分和沉积环境分析,对笔石与页岩气之间的关系研究甚少。充分利用取心井岩心分析资料、钻井地质资料、实验分析资料和测录井资料,结合不同沉积环境的笔石类型,将JYDA-E井奥陶系五峰组分成4个笔石带(WF1-WF4)、志留系龙马溪组划成6个笔石带(LM1-LM7,LM2缺失),其中WF2-LM4的TOC含量高、有机孔隙发育,属于页岩气有利开发层段。研究发现:笔石的演化和有机质的富集具有相同的沉积环境;笔石的丰度和TOC、有机孔隙度以及气测全烃含量具有正相关关系,笔石的演化对页岩有机质丰度、有机孔的形成具有一定贡献,并在一定程度上影响其含气性,属于页岩气储层评价的一项重要指标。四川盆地五峰组-龙马溪组页岩气形成和笔石的形成演化存在成因上的关联,这对页岩气储层研究具有借鉴意义。

A Study on the Relationship Between Graptolites and Shale Gas in the Wufeng and Longmaxi Formations in the Sichuan Basin

Previous research on graptolites mainly focused on stratigraphic division and sedimentary environment analysis, but rarely on the relationship between graptolite and shale gas. Using data from core well analysis, drilling and core logging and experimental analysis, the Ordovician Wufeng Formation in the Sichuan Basin is divided into four graptolites zones (WF1-WF4), whilst the Silurian Longmaxi Formation is divided into nine graptolites zones (LM1-LM9).In the WF2-LM4 zones,TOC contents are high and organic pores are well developed, and thus these zones are favorable for shale gas exploitation. We found that the graptolite evolution and organic matter enrichment have the same depositional environment, and the abundance of graptolites is positively correlated with TOC, organic porosity, and total hydrocarbon content measured by gas. The evolution has a certain contribution to the organic matter content and organic pore formation in the shale, and somehow affects its gas-bearing properties, which is an important factor in shale gas reservoir evaluation. The shale gas formation in the Wufeng and Longmaxi Formations in the Sichuan Basin was likely related to the formation and evolution of graptolites, which has major implications for shale gas reservoir studies.