## 5 Discussion
### Major Minerals Content vs. XRD  
We removed pore/kerogen and unclassified components from the corrected results, and then compared the identified mineral content results after normalizing with the XRD test results (Table 3). For comparison under the same unit system, the mineral mass percentage results measured by XRD were converted to volume percentage with the following equation:  
\[vol_{i}=\frac{w_{i}/\rho_{i}}{\sum_{i=1}^{n}w_{i}/\rho_{i}}\times 100 \tag{5}\]  
where \(vol_{i}\) is the mineral volume percentage, vol.%, \(w_{i}\) is the mineral mass percentage, wt.%, and \(\rho_{i}\) is the mineral density, g/cm\({}^{3}\). Note that the content of the illite-smectite mixed-layer (I/Smix) was calculated according to the mixed layer ratio I/S (%S) with the following equation:  
\[\rho_{I/S}=\frac{I/S}{1+I/S}\times\rho_{\mathrm{Illite}}+\frac{1}{1+I/S}\times \rho_{\mathrm{Smectite}} \tag{6}\]  
where \(\rho_{I/S}\) is the density of the illite-smectite mixed-layer, g/cm\({}^{3}\), \(I/S\) is the mixed layer ratio, a decimal with value of 0.1, \(\rho_{\mathrm{Illite}}\) is the illite density, g/cm\({}^{3}\), and \(\rho_{\mathrm{Smectite}}\) is the smectite density, g/cm\({}^{3}\). Since QEMSCAN identifies more mineral species than XRD, we simplified the QEMSCAN results, including classifying mica as clay minerals and combining illite and smectite. Image correction did not result in significant changes in the major mineral contents. Overall, the clay mineral and non-clay mineral contents identified by the QEMSCAN technique were comparable to the XRD results. Because of heterogeneity, from 2D to 3D, there must be a difference between the mineral content identified by the image and that measured by X-ray diffraction. For example, for quartz content, the QEMSCAN, corrected and XRD results were 18.31%, 21.63% and 31.09%, respectively (Table 3). For clay minerals, QEMSCAN can effectively identify mixed-layer clay minerals. Considering the uncertainties in identification and possible error determination on the illite-smectite mixed-layer and illite mineral in the interpretation process, the composition and content of clay minerals identified by QEMSCAN were similar to XRD, and the corrected clay mineral content was significantly closer to the XRD results. Reducing the error caused by dimension switching is an important research point in the future. According to the above analysis, the shale mineral analysis method fully combines the advantages of the most advanced mineral quantitative analyses, QEMSCAN technology, and high-resolution large-scale backscatter scanning electron microscopy analysis technology, and corrects the quantitative analysis results of QEMSCAN minerals using image smoothing, image alignment, image segmentation, and morphological analysis, and obtains the high-precision 2D quantitative distribution of shale minerals. In particular, it can effectively correct the content of clay minerals, pores, and organic matter components,and restore particle morphology and boundaries, among other parameters. This approach overcomes the shortcomings of conventional shale mineral analysis methods and shows obvious advantages. Based on the high-precision mineral distribution obtained by this method, its application can be further expanded, such as for counting the particle size distribution of various minerals, analyzing the distribution trends of organic matter or pores, and using random modeling methods to establish a 3D distribution model of shale minerals. This can further provide support for comprehensive shale reservoir evaluation, prospective zone prediction, fracturing transformation, and other shale-related evaluations. At present, the use of this method has only been carried out in preliminary exploration and research work. The classification of minerals (that is, the selection of correction methods), and the selection of correction parameters, are affected by human subjectivity, actual mineral distribution characteristics, and other factors.