## 2 Establishment of an Evaluation Index System for CBM Development
### Selection of CBM Development Block Indices
The #2, #8, and #9 coal seams in the Gujiao block all have CBM resources. The proven reserves of CBM resources in the Gujiao block are \(820\times 10^{8}\) m\({}^{3}\), and the average daily gas production per well is \(0.065\times 10^{4}\) m\({}^{3}\)[51]. The Daning-Jixian block with an area of 600 km\({}^{2}\) is located in the south of the Hedong coalfield, which belongs to the southern section of the western Shanxi ruffled belt in the eastern part of Ordos Basin. The #5 coal seam mainly formed in the sedimentary environment controlled by the land-based delta, especially in the area between Wucheng-Yaoqu a thick coal-rich belt formed, was conducive to the formation of higher CBM resource abundance. The caprock is dominated by fine sandstone and mudstone with different thickness and great variation. Siltstone and argillaceous sandstone exist locally, which results in medium sealing conditions. The proven reserves of CBM in this block are 295 \(\times\) 10\({}^{8}\) m\({}^{3}\)[52]. In this block, the anticline axis of Guyi-Yaoqu is swelled by the structure and the stress is reduced due to the release. The tectonic movement causes secondary fractures and microcracks in the coal seam to develop, which is conducive to the production of CBM, and the average daily gas production per well is \(0.2\times 10^{4}\) m\({}^{3}\)[4]. The Fengrun block with an area of 547 km\({}^{2}\) is located in the southern part of the Ningwu coalfield, Shanxi Province, which belongs to the turning end of the complex syncline structure. The immediate roof of the #9 coal seam is mainly composed of sandstone and mudstone, containing a small amount of limestone, and the roof is broken, which leads to the low gas content in this block. The coal seam is in a low-stress zone and is buried relatively shallow. Tensile fissures develop, and the permeability is extremely low, which has an adverse effect on CBM production. The proven reserves of the CBM resources in the Fengrun block are \(221\times 10^{8}\) m\({}^{3}\), and the average daily gas production per well is \(0.0729\times 10^{4}\) m\({}^{3}\)[53; 54]. Based on the existing exploration data, the main coal seam evaluation indices for each exploration site in each block were selected. The representative CBM exploration index values were selected as the indicator intervals for evaluation in this research. Specific indicator interval values are shown in Table 1. According to the evaluation index information in Table 1, the average value and gray standard deviation histogram of the evaluation parameters of target blocks are listed in Figure 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Category** & **Reservoir** & **Gas Content** & **Reservoir** & **Reservoir Pressure** & **Critical** & **Permability** & **Reservoir** & **Young’s** \\
**Depth/m** & **/m/\({}^{\prime}\)A** & **Tickness/m** & **Gradient/MP/100 m** & **Reservoir Ratio** & **/\(\lambda\)10-9 \(\mu\)m  
Figure 2 shows that, in the evaluation index information of the five target blocks, the four evaluation values in Block 1 have the largest fluctuation values for the reservoir thickness, critical reservoir ratio, permeability, and Young's modulus, with gray standard deviations of 0.94 m, 0.13, \(0.29\times 10^{-3}\)\(\mu\)m\({}^{2}\), and 280 MPa. These results show that the occurrence conditions of Block 1 are more variable than those of the other blocks, and the sampling data fluctuate greatly, which leads to instability of the evaluation indices.