Characterization of Refracturing Fracture Geometry and Production-Parameter Optimization Design for Low-Productivity Horizontal Shale Gas Wells in the H Block of Fuling

Refracturing is an important stimulation technique for improving the productivity of mature shale gas wells. However, for low-productivity horizontal wells, the controlling effects of production history and pre-refracturing energy replenishment on fracture re-initiation and repropagation remain insufficiently quantified. This study focuses on mature wells in the H Block of the Fuling shale gas field. The Jiaoshiba area in the Fuling shale gas field, located on the eastern margin of the Sichuan Basin, is characterized by organic-rich marine shales of the Wufeng–Longmaxi Formation, where gas enrichment is jointly controlled by the Jiaoshiba anticline, fault distribution, and favorable preservation conditions. A three-dimensional geological model was constructed using seismic interpretation, well logging, core analysis, ant-tracking fracture attributes, and field fracturing data. A one-way coupled finite-element workflow was then applied to simulate the evolution of pore pressure and in situ stress during primary production, water-injection energy replenishment, and refracturing. The model was calibrated against historical bottomhole flowing pressure data, with a pressure-response matching accuracy greater than 85%. The results show that a lower initial production (4 × 104 m3/d) allocation can mitigate reservoir pressure depletion and maintain a more favorable stress environment for fracture branching during refracturing. Compared with refracturing after 10 or 20 years of production, refracturing after 5 years produced a stronger post-treatment response in the simulated cases. For water-injection energy replenishment, an injection rate of 700 m3/d restored reservoir pressure and regulated the local stress field more effectively than 500 m3/d, whereas increasing the rate to 1000 m3/d provided only limited additional pressure recovery. Overall, under the simulated reservoir conditions, a technically favorable parameter combination for the target well is an initial production allocation of 4 × 104 m3/d, refracturing after approximately 5 years of production, and one year of pre-refracturing water-injection energy replenishment at about 700 m3/d. These findings provide a reference for refracturing timing and pre-treatment energy-replenishment design in depleted shale gas reservoirs.