## 2 Establishment of an Evaluation Index System for CBM Development
### Selection of CBM Development Block Indices  
Based on the selected eight resources and productivity characterization indices, the following blocks were selected for this research: The Fanzhuang-Zhengzhuang block in the southern Qinshui coalfield, the Sanjiao block in the central Hedong coalfield, the Gujiao block in the northern Xishan coalfield, the Daning-Jixian block in the southern Hedong coalfield, and the Fengrun block in the southern Ningwu coalfield. Five CBM test blocks, with areas of 547 km\({}^{2}\) to 675 km\({}^{2}\), were evaluated as target blocks sorted in the order of Block 1, Block 2, Block 3, Block 4, and Block 5, as shown in Figure 1.  
The main coal seam in Shanxi is the Carboniferous-Permian coal-bearing formation, which occurred mainly during the tectonic movements of the Indosinian, Yanshanian, and Himalayan periods, respectively, among which the Yanshanian period was the most active. The Fanzhuan-Zhengzhuang block is located in the south of Qinshui coalfield, Shanxi Province, and belongs to the groundwater retention area, which provides a suitable hydrogeological condition for the preservation of CBM. The #3 coal seam in the Fanzhuang-Zhengzhuang block has a high degree of thermal evolution, and the degree of metamorphism is in the lean coal-anthracite stage. The coal seam has high gas generating capacity and adsorption capacity, resulting in high gas content. The resource area of the Fanzhuang-Zhengzhuang block is 666 km\({}^{2}\) and the proved reserves of the CBM in this block are \(861.65\times 10^{8}\) m\({}^{3}\)[42]. The top and bottom of the coal seam are well-se  
Figure 1: Shanxi location and target blocks location map. conducive to the storage of CBM. In this block, the critical reservoir ratio is relatively large, indicating that the desorption pressure is close to reservoir pressure, which shortens the desorption time of CBM, and increases the effective desorption area and production. Because of the large proportion of micropores and small pores in the coal sample, resulting in low permeability [43; 44]. However, the widespread development of exogenous fissures makes up for the deficiency of pore development, which causes the CBM of this block to form a high yield, and the average daily gas production per well is \(0.2218\times 10^{4}\) m\({}^{3}\)[45]. The Sanjiao block is a type of gently inclined structure which is located in the middle of the Hedong coalfield, Shanxi Province. The #3 + #4 + #5 coal seam in the Sanjiao block has low permeability mudstone roof strata, which are compact and intact, forming a closed, controlled, tectonic setting, preventing the escape of CBM, and maintaining a high gas content in the coal seam [46]. At the same time, the pores in the coal body are well developed, and the macropore contents are as high as 49.8%, which leads to a relatively high permeability in this area and increases the radius of the drainage and depressurization funnel in the production process of CBM wells, which is conducive to the migration of methane [47]. The resource area of the Sanjiao block is 675 km\({}^{2}\), the CBM resource reserve in the main coal seam is \(532.7\times 10^{8}\) m\({}^{3}\), and the average daily gas production per well is \(0.24\times 10^{4}\) m\({}^{3}\)[4; 48]. The Gujiao block with an area of 566 km\({}^{2}\) is located in the northern part of the Xishan coalfield, Shanxi Province, and the overall structural form is the Malan syncline. Multiple plastic deformations occurred in this block, resulting in a complicated structural shape, serious deformation, and a broken coal body in the #2 coal seam. Multiple stress releases cause the CBM to escape, thus reducing the gas content in the block [49]. The #2 coal in the Gujiao block is mainly bituminous coal of medium metamorphism. The coal quality is soft, and a large amount of pulverized coal can be easily produced under the action of external force, thus blocking the seepage passage, which has an adverse effect on the CBM production [50].