# A Study on the Remaining Reserves of the Weiyuan Shale Gas Block in Three-Dimensional Development
## 4 Target Layer Preferences  
The shale gas production contribution of the Longmaxi Formation in the Weiyuan block mainly comes from the sweet spot section of high-quality shale around 5 m, while outside the sweet spot section, the thickness of the layer with TOC > 2% exceeds 30 m. Currently, the main target of horizontal development of the Weiyuan shale gas block is the middle and lower part of the Longyi\({}_{1}\)\({}^{1}\) layer, and the analysis of logging monitoring data shows that the height of the artificial hydraulic fracture is only 10-15 m, and the vertical target mainly utilized the Wufeng-Longyi\({}_{1}\)\({}^{3}\) layer. The target layer for the three-dimensional development of Weiyuan shale gas should preferably be the layer in which there is a Class I reservoir of large thickness in the upper gas layer, which cannot be effectively reached by the fracturing layer network in the lower gas layer [35; 36; 37; 38]. Thus,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Platform** & **Number of Wells** & **Reserve** & **Well Control** & **Total Geological** & **Total Well** & **Average Remaining** \\  & **of Wells** & **Abundance/(10\({}^{8}\) m\({}^{3}\)\(\cdot\)km\({}^{-2}\))** & **Area/(km\({}^{2}\))** & **Reserves/(10\({}^{8}\) m\({}^{3}\))** & **Reserves/(10\({}^{8}\) m\({}^{3}\))** \\ \hline H64 & 5 & 5.25 & 2.64 & 13.86 & 5.84 & 1.60 \\ H6 & 6 & 4.71 & 3.37 & 15.87 & 9.05 & 1.14 \\ H16 & 8 & 5.33 & 4.26 & 22.71 & 10.91  
the Longyi\({}_{1}\)[1] layer, Longyi\({}_{1}\)[2] layer, and Longyi\({}_{1}\)[3] layer are excluded as the target layers for three-dimensional development. The reservoir of Longyi\({}_{1}\)[4] is relatively thick, 18-34 m. In order to finely characterize the reservoir of the Longyi\({}_{1}\)[4] layer, the Longyi\({}_{1}\)[4] layer is further subdivided into the Longyi\({}_{1}\)[4] minor layer, the Longyi\({}_{1}\)[4] minor layer, and the Longyi\({}_{1}\)[4] minor layer, based on the lithological and radiological characteristics. The overall recovery degree of the Longyi\({}_{1}\)[4] layer is low, and the stratigraphic pressure is kept relatively stable, and the production wells have not been effectively utilized, so the Longyi\({}_{1}\)[4] minor layer, Longyi\({}_{1}\)[4] minor layer, and Longyi\({}_{1}\)[4] minor layer are the main layers preferred for the vertical target of the upper gas layer for three-dimensional development. According to the standard of reservoir classification, the analysis of reservoir parameters of the Longyi\({}_{1}\)[4] layer found that the reservoir parameters of the Longyi\({}_{1}\)[4] minor layer are optimal, and it is the co-development of Class I+II reservoirs; the Longyi\({}_{1}\)[4] minor layer is the next best, and it mainly develops Class II reservoirs with thin layers of Class I reservoirs; and the quality of reservoirs of Longyi\({}_{1}\)[4] minor layer is comparatively poor, and it develops Class II+III reservoirs. The fracture model is generated with the joint constraints of the stress field and fracture strike model for the Longyi\({}_{1}\)[4] layer (Figure 6), and the analysis shows that the natural fracture density of the formation shows an overall decreasing trend from the Longyi\({}_{1}\)[4] minor layer to the Longyi\({}_{1}\)[4] minor layer. Among them, the natural fracture development of the Longyi\({}_{1}\)[4] minor layer is the best, and the natural fracture density can reach 1.42 m\({}^{-1}\). According to the reservoir quality and fracture density, the upper target should be preferred in the Longyi\({}_{1}\)[4] and Longyi\({}_{1}\)[4] minor layers. Development practices have shown that early fracture distribution characteristics and the direction of geostress can affect the fracturing effect of horizontal wells [39; 40; 41]. Therefore, the rock mechanical parameters affecting the artificial fracture network should also be considered when selecting the target.