渝东南地区五峰-龙马溪组页岩储层纳米孔隙发育特征及影响因素——以重庆石柱剖面为例

Nanopore Structure Characteristics and Impacting Factors of Wufeng-Longmaxi Formation Shale in Southeast Chongqing:A Case Study of Shizhu Outcrop

孔隙结构特征是页岩气富集与保存的重要研究内容之一。以渝东南地区重庆石柱剖面五峰-龙马溪组页岩为研究对象,综合有机碳含量、矿物组成、孔径分布和孔隙类型等方面对研究区页岩储层进行了系统表征,进一步明确了影响页岩储层纳米孔隙发育的主要因素,并探讨了其实际地质意义。结果表明,重庆石柱剖面五峰组和龙马溪组龙一1小层页岩内有机碳含量高,达到4.8%,矿物成分以石英为主,黏土矿物次之,且含少量的长石和碳酸盐岩。页岩孔径分布呈双峰型,主要分布于0.3~0.9 nm的微孔和60~100 nm及200~300 nm的宏孔。五峰-龙马溪组页岩内有机孔极为发育,黏土矿物层间孔、石英及方解石粒内溶蚀孔和黄铁矿晶间孔均有发育,这些孔隙为页岩气的保存与富集提供了储集空间。其中微孔和介孔控制着比表面积大小,介孔和宏孔对孔体积的贡献显著。研究区页岩纳米孔隙发育主要受有机碳含量和矿物组成控制,具体体现在:页岩内有机碳含量与孔体积和比表面积呈现良好的正相关,尤以微孔和介孔最为明显。黏土矿物和碳酸盐岩与微孔和介孔体积具有正相关,石英含量与孔体积呈负相关,突出表现在与微孔、介孔体积强负相关。

Pore structure characteristics are one of the important research contents of shale gas enrichment and preservation.Taking Wufeng-Longmaxi Formation shale of Shizhu section in southeastern Chongqing as the research object,the shale reservoir in the study area was systematically characterized by organic carbon content,mineral composition,pore size distribution and pore type.The main factors affecting the nano porosity development of shale reservoir were further clarified,and its practical geological significance was discussed.The results show that Wufeng Formation and Long11 of Longmaxi Formation in Chongqing Shizhu section has high organic carbon content(4.8%).The mineral composition is dominated by quartz,followed by clay minerals,and contains a small amount of feldspar and carbonate rocks.The pore size distribution of shale is bimodal,mainly distributed in the micropores of 0.3~0.9 nm and the macropores of 60~100 nm and 200~300 nm.Organic pores are extremely developed in the Wufeng-Longmaxi Formation shale,interlayer pores of clay mineral,dissolution pores in quartz and calcite grains,and intercrystalline pores of pyrite are all developed.These pores provide storage space for the preservation and enrichment of shale gas.The specific surface area is controlled by micropores and mesopores,and the pore volume is significantly dominated by the contribution of mesopores and macropores.It is embodied in the fact that total organic carbon content in shale has a good positive correlation with pore volume and specific surface area,especially micropores and mesopores.Clay minerals and carbonate rocks also have a positive correlation with micropores and mesopores volume,and the quartz content has a negative correlation with the pore volume,which is prominent in the strong negative correlation with micropores and mesopores.