## 3 Methods  
### TOC, Mineralogical Analysis, and SEM  
Organic carbon content analysis is a common method to determine the abundance of organic matter in shale. The test implementation standard in this paper is the \"determination of total organic carbon in sedimentary rocks\" (GB/T19145-2022) [23]. The shale sample was weighed to determine its mass, which was found to be 5 g. Subsequently, the sample was ground into a fine powder with a particle size of 200 mesh using an agate mortar. The powdered sample was placed into a beaker and immersed in hydrochloric acid in order to eliminate carbonate minerals and other minerals that are soluble in acid from the sample. Subsequently, the substance was subjected to multiple washes utilizing deionized water until the resulting solution attained a state of neutrality. The remaining samples were subjected to a drying process in a controlled environment at a consistent temperature of 60 \({}^{\circ}\)C. Subsequently, the EURO 3000 elemental analyzer was utilized to determine the organic carbon content of the aforementioned samples. The reflectance of vitrinite was measured by an MPV-SP microphotometer at room temperature of 23 \({}^{\circ}\)C and relative humidity below 70%. The reflected light and UV fluorescence mode were used to identify the macerals, and we referred to Xiao for the classification of the materials [24]. Before the start of the vitrinite reflectance (Ro) measurement experiment, two standard samples were used to correct the instrument, and the R\({}_{\rm O}\) values were 0.59% and 1.72%, respectively. The vitrinite observation and reflectivity measurement of the sample were carried out with a 50X oil immersion objective lens. The measurement of R\({}_{\rm O}\) value generally needs to be carried out on the larger and more homogeneous vitrinite. Since there are few vitrinite fragments in continental shale, in order to measure reliable R\({}_{\rm O}\) data, it was necessary to measure the reflectance of multiple vitrinite fragments at least 20 times to obtain the average vitrinite reflection value of the sample. To elucidate the mineral composition characteristics of shale within the study area, X-ray diffraction (XRD) analysis data were subjected to statistical analysis in this research. The testing protocol adhered to the standards outlined in \"X-ray Diffraction Analysis Method for Clay Minerals and Common Non-Clay Minerals in Sedimentary Rocks\" (SY/T5163-2018) [25]. XRD analysis is a highly valuable technique utilized for the identification and quantification of minerals present in shale samples. Through the utilization of a statistical analysis of XRD data, scholars are able to acquire valuable knowledge regarding the mineralogical composition of shale formations. This knowledge plays a crucial role in comprehending the properties and potential applications of these formations. The implementation of a standardized approach in this study area guarantees the dependability and uniformity of the mineral composition data acquired from the shale samples. The XRD experimental apparatus employed in this study is a high-resolution diffractometer known as the SmartLab X-ray diffractometer [26]. This instrument is produced by Riken Science and Technology Corporation, a reputable manufacturer based in Japan. Weigh 2 g of shale sample and grind it into a powder with a particle size of less than 200 mesh in an agate mortar, then proceed to the next step. In order to ascertain the mineral composition of the shale, it is recommended to fabricate a measurement test specimen utilizing the back-pressure technique. Weigh a 20 g sample of shale, place it into distilled water, and stir to suspend. Extract the suspension and obtain clay mineral samples using a centrifuge; then, carefully slice them into a natural form. The distillation of ethylene glycol should be conducted using unaltered samples, and the resultant distilled samples should be subjected to elevated temperatures using a muffle furnace.