# A Study on the Remaining Reserves of the Weiyuan Shale Gas Block in Three-Dimensional Development
## 1 Introduction  
Shale gas contains organic matter-rich mud shale in the state of adsorbed and free gas, which can form self-generated and self-stored continuous gas reservoirs, but the shale segments need to be fractured to form reticulated cracks for effective production [1]. Since the establishment of the Weiyuan block as a national shale gas demonstration area in March 2012 [2], the development of the Weiyuan block has so far involved the formulation and implementation of five development programs, and by the end of 2023, there were a total of 489 production wells, with an annual production of 4 billion cubic meters, and the cumulative production exceeded 23.6 billion cubic meters. Years of development practices have shown that the effectiveness of shale gas development is correlated with the degree of drilling and completion and fracture modification [3]. At the early stage of the development of the Weiyuan block, due to the limited understanding of the stratigraphyand the low level of engineering technology (the length of the horizontal section is only 1500 m, the drilling encounter rate of the target body is 50%, and the strength of the sand added is less than 1.5 t/m), resulting in unsatisfactory mining results and low utilized reserves, with the utilized reserves of the Wufeng-Longyi 1 subsection reserves being less than 30% [4; 5; 6]. Aiming at the remaining gas development potential of the Weiyuan block, a three-dimensional development is proposed as a countermeasure to improve the utilized reserves.  
Three-dimensional development refers to the deployment of a multi-layer horizontal well network based on the shale's depositional characteristics, reservoir characteristics, and sweet spot distribution, to expand the fracture network's reach volume to a greater extent, to effectively increase the degree of vertical mobilization of shale gas reservoirs, and to improve the benefits of shale gas development [7; 8]. The Weiyuan block is similar to the Wufeng-Longyi 1 subsection shale gas layer in China, which has been implemented in three-dimensional development blocks [9; 10; 11; 12] and has three-dimensional development geological conditions. Slit-height monitoring in Weiyuan indicates that all high-quality vertical shale segments are difficult to accommodate by a horizontal well network, with potential for residual gas development. The Weiyuan block has a low technical level at the early stage of development, with insufficient capacity for reservoir transformation, and there is room for reservoir transformation. Therefore, the Weiyuan block has preliminary conditions for three-dimensional development to tap the remaining reserves. In the domestic practice of three-dimensional development effect (Figure 1), the minimum recovery factor increase is 7%, the maximum is 32%, and the average is 15%. The application cases of each three-dimensional development block show that three-dimensional development is an important way to improve shale gas recovery. In order to improve the utilized reserves in the study area, this paper analyzes the remaining shale gas reserves in the Weiyuan block and takes three-dimensional development as a countermeasure to improve the utilized reserves, with a view to providing a reference for the three-dimensional development strategy of the Weiyuan shale gas block.