# Weight Assignment Method and Application of Key Parameters in Shale Gas Resource Evaluation
## 5 Case Applications  
The Jiaoshiba area in the Sichuan Basin is located in the southeastern part of the Sichuan Basin, with a structural location in the southern uplift section of the Wanxian syncline in the steep fold belt of the eastern Sichuan Basin. The steep fold belt in Eastern Sichuan is an important gas-producing area in the Sichuan Basin. The surrounding areas mainly develop reverse faults, with good conditions for reservoir formation and preservation. They mainly develop deep-water shelf facies, which are in the early stage of over maturity. They mainly develop nano-scale organic pores and micropores between clay minerals, and the fracture system is not developed, which is conducive to the enrichment and preservation of shale gas [37,38]. The high and steep fold belt in Eastern Sichuan runs from the south to the north, with a structural trend from the NNW to NNE, and then to the NE, forming the most distinctive arc-shaped fold belt in the Sichuan Basin. The Jiaoshiba block is mainly located in the southern part of the Wanxian syncline, a third-level structural unit. Overall, it is wide in the south and narrow in the north, wide in the middle, and gentle in the NE direction. It intersects with the Fangdoushan anticline of the third-level structural unit on the west side. The main structure is a box-shaped anticline, which is relatively stable. The boundary faults are mostly reverse faults, with good sealing, a high pressure coefficient, and good preservation conditions [39]. The shale gas layer is composed of the Upper Ordovician Wufeng Formation to the Lower Silurian Longmaxi Formation Longyi Member, mainly developed in deep-water continental shelf facies. The lithology is mainly composed of grey black radiolarian carbonaceous graclite shale and carbonaceous siltstone shale; it is vertically distributed continuously with a total thickness ranging from 70.1 to 86.6 m. The organic matter type is mainly type I, with a TOC content ranging from 0.46% to 7.13% with an average of 2.66%. The Ro value ranges from 2.2% to 3.1%, indicating an early stage of over maturity. The content of brittle minerals is high, ranging from 33.9% to 90.3% with an average of 56.5%, which is beneficial for later transformation. The porosity of shale gas reservoirs ranges from 1.17% to 8.61% with an average of 4.87%. The on-site gas content ranges from 0.63% to 9.63% \(\mathrm{m^{3}/t}\) with an average of 4.61 \(\mathrm{m^{3}/t}\)[40,41,42,43,44,45,46,47,48,49]. The Jiaoshiba area of the Fuling shale gas field belongs to an area with a high exploration degree, and the upper gas layer in the Jiaoshiba area of the Fuling shale gas field does not contain crude oil. Therefore, the volume method should be used to calculate the adsorbed gas resources [50,51]. According to the basic principle of the probability volume method, shale gas resources are the probability product of shale mass and the natural gas content (gas content) per unit mass of shale. The specific formula is as follows:  
\[Q=A\cdot h\cdot\rho\cdot q \tag{6}\]  
where Q is the shale gas resource, A is the gas bearing shale area (km\({}^{2}\)), h is the effective shale thickness (m), \(\rho\) is the shale density (t/m\({}^{3}\)), and q is the gas content (m\({}^{3}\)/t). Among them, the calculation of the gas content, q, is relatively complex, and the decomposition method can be used to separately calculate the (total) gas content. In the shale layer system, the occurrence mode of natural gas may be in the free, adsorbed, or dissolved state, and different methods can be used for calculation. The discussion on gas content data is not the focus of this article, so only existing data will be used for method introduction here. The data source of this article is the data obtained by the author's team in 2019. After preliminary data processing and screening, 20 original data points were selected for instance application (Table 8). Organize the parameters into matrices:  
\[[X]=