Numerical investigation of superheated steam injection for in situ oil shale exploitation: fracture network optimization and energy efficiency analysis

This study numerically investigates in situ oil shale exploitation by superheated steam injection, emphasizing coupled thermo-hydraulic-mechanical processes. An anisotropic multi-field model was developed to evaluate how hydraulic fracture distribution and thermally activated weak planes affect oil/gas recovery and energy return. Using conditions from the Balikun deposit (Xinjiang), four cases were simulated (1–2 hydraulic fractures, with/without weak-plane evolution). Weak-plane activation markedly improves heating via alternating convection and conduction, expanding high-temperature zones and achieving 90.5% oil recovery after 1000 days. Without it, heating is limited (< 60% recovery) and production declines rapidly. Energy return rates peak early (5.79–8.44) but decay without fracture evolution, whereas activated weak planes sustain values > 5 for over a year. Doubling initial fractures boosts recovery by 46% but only slightly improves energy efficiency due to higher steam consumption.