Inter-well interference and well spacing optimization in Weirong shale gas field in Sichuan Basin, China

Optimal well spacing is crucial for maximizing single-well productivity and efficiently utilizing reserves, making it a core indicator for evaluating development effectiveness. Due to the influence of natural fractures and the production sequence, the annual well opening pressure and inter-well interference in the Weirong Gas Field have led to an intensifying year-on-year decline, which have seriously affected both production and construction outcomes. To reduce inter well interference and improve productivity and construction efficiency, this study analyzes the interference mechanisms between wells. The results show that the main causes of interference are natural fractures and older well energy depletion. Based on these insights, a numerical simulation method was used to quantitatively evaluate the impact of varying well spacing, degrees of fracture hit and cumulative gas production from older wells on the Estimated Ultimate Recovery (EUR) of new wells. Consequently, a targeted and differentiated well spacing optimization design method was developed. The results show that: (1) The smaller the well spacing and the higher the degree of fracture hit, the greater the decrease on the EUR of new wells, with impact degrees of 7.1%–15.1%; (2) The smaller the well spacing and the higher the cumulative gas production from older wells, the greater the negative impact on the EUR of new wells, ranging from 8.1% to 28.3%; (3) In areas with well-developed natural fractures, a recommended well spacing of 350–450 m is suggested based on the fracture hit degree; (4) Near older wells, where energy depletion is prominent, a well spacing of 400–500 m is recommended. Following the application of well spacing optimization, the average well opening pressure increased by 9.3 MPa, and the EUR improved by 22.8%, demonstrating a favorable application effect and providing reference for well pattern arrangement in similar shale gas reservoirs.