Evaluation of shale gas reserve recoverability and three-dimensional development potential: a case study of the Weiyuan Block, Sichuan basin
摘要
The primary horizontal well network in the Weiyuan block is vertically deployed in the Long111 sub-layer, and it is difficult to fully utilize the 43.9–53.6 m thick Wufeng formation-Long11 sub-member. To enhance the reserves utilization degree, this study proposes a method for evaluating the vertical utilized degree of shale gas reserves based on the calibrated estimated ultimate recovery (EUR) iterative utilized thickness and a quantitative evaluation method of shale gas reservoir productivity based on reservoir classification. The reserves utilization degree and vertical utilization thickness of the primary well network in the Weiyuan block are evaluated, the distribution characteristics of remaining reserves are clarified, and the three-dimensional development potential is analyzed. The results show that: (1) The horizontal well hydraulic fracture network of the primary well network in the production area mainly utilized the Wufeng formation-Long113 sub-layer, and the utilized thickness is between 3.49 and 19.40 m, with an average of 13.79 m. Vertically, only 30% of the reservoir is utilized. (2) The well-control reserve recovery of the primary well network in the production area is 75%, the average EUR of half-branch wells is 0.87 × 108 m3, the average well-control geological reserves of half-branch wells are 1.16 × 108 m3, and the total well-controlled geological reserves in the whole area are 906.7 × 108 m3. (3) The total remaining geological reserves are 1690.5 × 108 m3, the average remaining reserves abundance is 4.31 × 108 m3/km2, the average thickness of unutilized reserves is 26.16 m, and the high-value areas are all located in the eastern part of the production area. (4) Under the condition of the same thickness, the ratio of gas production capacity of Type I and Type II reservoirs is 3.7:1. (5) According to the favorable area screening principle, the favorable area is screened out to be 116.7 km2, and the total geological reserves are 700.7 × 108 m3. This study provides a new development idea for improving shale gas production in the Weiyuan block.