The significantly different geological processes experienced by the shales in the southern Sichuan Basin provide a means for comparing their pore characteristics and their supercritical methane adsorption capacities. In this study, we analyzed the Wufeng Formation (O₃w)–Longmaxi Formation (S₁l) shales in the southern Sichuan Basin using multiple analytical methods, including mineralogy, field emission scanning electron microscopy (FE-SEM), mercury intrusion capillary pressure (MICP), low-pressure gas adsorption (LPGA), and high-pressure methane adsorption. Four types of shale lithofacies were identified including clay-rich siliceous shale (S-3), argillaceous/siliceous mixed shale (M-2), silica-rich argillaceous shale (CM-1), and mixed argillaceous shale (CM-2). With increasing burial depth, the pore system gradually shifted from organic matter (OM) pores to intergranular (interP) pores between the OM clumps and the brittle minerals. The results of the MICP and LPGA were not significantly affected by burial depth, but were closely related to the total organic carbon (TOC) content and lithofacies. The surface areas and total pore volumes (V_p’s) varied from 5.44 to 11.73 m²/g with an average of 9.89 m²/g and from 0.88 to 2.04 cm³/100 g, respectively. Patterns in the V_p and surface area values of the S-3 and M-2 samples exhibited four-modal features, while the CM samples were bimodal. The excess adsorption capacity reached its maximum value when the pressure was about 9–11 MPa, and then it decreased as the pressure increased. The mesopores provided the main V_p (average 43.1%), and the micropores provided the main surface area (average 74.38%). The adsorption positions of the gas molecules can be provided by micropores and mesopores, and even by microcracks and macropores, and as the TOC content of the shale increases, the contribution of the micropores to adsorption becomes more significant.

中文翻译：

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川南地区五峰组-龙马溪组页岩不同岩相孔隙特征及甲烷吸附能力

四川盆地南部页岩经历的明显不同的地质过程为比较其孔隙特征和超临界甲烷吸附能力提供了一种手段。在这项研究中，我们分析了五峰组（O ₃ w）-龙马溪组（S ₁l）四川盆地南部的页岩采用多种分析方法，包括矿物学，场发射扫描电子显微镜（FE-SEM），压汞毛细管压力（MICP），低压气体吸附（LPGA）和高压甲烷吸附。确定了四种类型的页岩岩相，包括富含粘土的硅质页岩（S-3），泥质/硅质混合页岩（M-2），富含二氧化硅的泥质页岩（CM-1）和混合泥质页岩（CM-2）。 。随着埋藏深度的增加，孔隙系统逐渐从有机质（OM）孔隙转移到OM团块与脆性矿物之间的粒间（interP）孔隙。MICP和LPGA的结果不受埋藏深度的影响不明显，但与总有机碳（TOC）含量和岩相密切相关。V _p的）从5.44变化到11.73米² /克，平均9.89米² / g和0.88〜2.04厘米³ / 100g时，分别。S-3和M-2样品的V _p和表面积值的模式表现出四峰特征，而CM样品为双峰特征。当压力约为9-11 MPa时，多余的吸附容量达到最大值，然后随着压力的增加而减小。中孔提供了主要的V _p（平均43.1％），而微孔提供了主表面积（平均74.38％）。气体分子的吸附位置可以由微孔和中孔提供，甚至由微裂纹和大孔提供，并且随着页岩中TOC含量的增加，微孔对吸附的作用变得更加明显。