## 1 Introduction  
Oil and gas are mainly stored in free and adsorbed states in shale reservoirs. In recent years, with an expansion in unconventional oil and gas exploration and development, the traditional understanding of shale as being primarily only a source and caprock has shifted due to the discovery of an abundance of oil and gas resources [1]. Minerals in shale directly control the development of microporous networks and have critical influences on the porosity, hydrocarbon content, and permeability of shale [2; 3; 4; 5]. Minerals in shale mainly include, but are not limited to, quartz, feldspar, and clay, as well as small amounts of calcite and dolomite. The brittleness of minerals such as quartz and calcite under extreme external stress facilitates the creation of cracks, which, in turn, become important seepage channels for oil and gas. Because clay minerals have a larger specific surface area and a stronger adsorption capacity than quartz and calcite [6], shale oil and gas can also be preserved in an adsorbed state. The mineral composition provides the material basis for the formation and evolution of shale pores and is an important factor in the accumulation of shale hydrocarbons. Accordingly, shale mineral analysis has significant relevance in determining the diagenetic evolution, reservoir evaluation, target location identification, and the fracturing transformation of shale. The mineral analysis is mainly inclusive of mineral composition, morphology, and distribution. The main conventional shale mineral analysis methods are rock petrographic analysis, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and focused ion beam scanning electron microscopy (FIB-SEM), among others. Based on differences in principles and techniques, these methods each have their own applicability, as well as their own advantages and disadvantages. For example, petrographic analysis is mainly used for rock type classification, mineral structure and composition determination and diagenesis in the study of mineralogy and the evaluation of formations. The main disadvantages of this method are that, through manual (human) observation, bias/errors can be generated, and the resolution prevents mineral analysis and micropore morphology and mineral morphology characterization [7]. XRD can determine the composition of various minerals; however, it cannot assess mineral distribution, nor identify mineral morphology [8]. FESEM may, under high resolution, provide rock mineralogy validation and morphology; however, it cannot execute quantitative characterization [9]. FIB-SEM, along with various computerized tomography (CT) scans, can obtain 3D spatial distribution images of minerals; however, the field of view is not large. Furthermore, it would not only be unable to provide the mineral composition but also the quantitative characterization of the morphology [10]. The methods mentioned above mostly focus on assessing mineral composition or producing scanned images of mineral distribution and morphology. However, there is difficulty in determining the quantitative characterization while retaining mineral morphology and distribution. Moreover, it is also impossible to directly obtain the content and distribution of various types of organic matter, pores, and fissures in shale. In addition, X-ray fluorescence spectrometry (XRF) can be used for mineral analysis, in combination with XRD or SEM [11]. XRF enables high-resolution (up to 1 ppm), fast and accurate acquisition of most elemental species and their relative content on the sample surface. But the quantitative analysis of XRF has an error of 5-10%, and the conversion of elemental content to mineral content is subject to error and requires a large number of standard samples for calibration. Consequently, definite challenges and constraints still exist in developing precise shale mineral characterization or quantification studies through these methods.