Abstract:

Organic matter pores serve as the primary spaces for shale gas enrichment and accumulation,and their developmental characteristics are crucial for reservoir evaluation and selection. However,current research on the combinations,characteristics,and heterogeneity of mineral-organic matter pores remains relatively limited. This study focuses on the Longmaxi Formation and Wufeng Formation shales in the southern Sichuan Basin region,employing a suite of techniques including whole-rock X-ray diffraction analysis,argon ion polishing-scanning electron microscopy,electron micro-probe analysis,cathodoluminescence,and Image J image analysis. These methods are used to elucidate the relationships between minerals and organic matter,describe the structural characteristics of mineral-organic matter pore combinations,analyze the distribution patterns of these combinations across different lithofacies,and investigate the impact of their heterogeneous distribution on shale reservoir properties.The results reveal the following key findings: (1)Quartz,clay minerals,carbonate minerals,and pyrite exhibit multiple occurrence relationships with organic matter in shale,and a total of four categories comprising 12 types of mineral-organic matter pore combinations were identified;(2)The distribution of mineral-organic matter pore combinations varies among different lithofacies. Biogenic siliceous shale is predominantly characterized by quartz-organic matter pore combinations,with a relative content of 73.59%. Clay shale,feldspathic-calcareous siltstone,calcareous shale,and feldspathic siltstone are mainly dominated by clay mineral-organic matter pore combinations,with relative contents of 73.45%,55.45%,38.92%,and 53.66%,respectively. Calcareous siltstone is primarily characterized by carbonate mineral-organic matter pore combinations,with a relative content of 55.01%;(3)Organic matter encapsulated within quartz and clay minerals exhibits a flow structure,characterized by high organic matter content,large pore size,high porosity,and good pore connectivity. These pore types are the most favorable for reservoir development;(4)Biogenic siliceous shale is identified as the optimal shale gas reservoir,and its high gas content(3.53m³/t)aligns closely with the high relative abundance(33.71%)of favorable mineral-organic matter pore combinations. In conclusion,the distribution characteristics of mineral-organic matter pore combinations significantly influence the gas content of shale,and the relative content of favorable pore combinations is positively correlated with gas content. This finding holds substantial implications for the evaluation and selection of shale gas reservoirs.

Key words: Wufeng and Longmaxi formations, mineral-organic matter pore combination, shale reservoir, lithofacies, heterogeneity, shale gas enrichment

摘要：

有机质孔是页岩气赋存、富集的主要空间,其发育特征对于储集层评价及优选具有重要意义,而目前关于矿物-有机质孔组合类型、特征及非均质性方面的研究较为薄弱。为此,以川南地区五峰组—龙马溪组页岩为研究对象,利用全岩-X衍射分析、氩离子抛光—扫描电镜、电子探针显微分析、阴极发光、Image J图像分析等手段,厘清矿物与有机质的赋存关系,刻画矿物-有机质孔组合结构特征,分析不同岩相的矿物-有机质孔组合分布特征,探讨矿物-有机质孔组合的非均质分布对页岩储集层的影响。研究结果表明: (1)石英、黏土矿物、碳酸盐矿物和黄铁矿与有机质各存在3种赋存关系,共识别出4类12种矿物-有机质孔组合; (2)矿物-有机质孔组合在不同岩相中的分布表现出差异性,生物硅质页岩以石英-有机质孔组合为主,相对含量为73.59%;黏土质页岩、长英质-钙质粉砂页岩、钙质页岩和长英质粉砂页岩以黏土矿物-有机质孔组合为主,相对含量分别为73.45%、55.45%、38.92%、53.66%;钙质粉砂页岩以碳酸盐矿物-有机质孔组合为主,相对含量为55.01%;(3)有机质包裹成岩石英和黏土矿物呈流动结构有机质孔的有机质相对含量高、孔径大、成孔率高、孔隙连通性好,是对储集层最有利的2类有机质孔; (4)生物硅质页岩是页岩气的最佳储集层,其中对储集层有利的矿物-有机质孔组合的相对含量高达33.71%,与其3.53 m³/t的高含气量相吻合。结论认为,矿物-有机质孔组合的分布特征影响页岩的含气性,对储集层有利的矿物-有机质孔组合的相对含量与含气量呈正相关关系,该认识对储集层评价具有重要意义。

关键词: 五峰组—龙马溪组, 矿物-有机质孔组合, 页岩储集层, 岩相, 非均质性, 页岩气富集

CLC Number: 

• TE122.221