Volume 60

Assessment of Heat Extraction and Fracture Behavior in Abandoned Reservoirs Zhipeng Wang, Yuanxin Zhang, Qidi Cheng

Abstract

Geothermal development in abandoned reservoirs with CO₂ recirculation aligns with energy-transition goals, yet more efficient system designs are needed. This study reconfigures multi-stage fractured horizontal well patterns into a fractured closed-loop geothermal system (FCLG), in which injection–production fractures interconnect to create multiple rows of high-conductivity channels for heat extraction. We build numerical models to compare a conventional closed-loop system (CLG), a conventional multi-stage fractured horizontal well system (MSFHW), and the proposed FCLG, and we obtain dynamic fracture conductivity from core displacement experiments under geothermal conditions. The multiphysics simulations reveal three characteristic production stages for FCLG: an initial plateau, a decline, and a secondary plateau. Sensitivity analysis indicates injection temperature governs heat-extraction efficiency most strongly, followed by injection flow rate and temperature difference; lower injection temperatures, lower flow rates, and larger temperature differences improve performance. Relative to MSFHW, FCLG delivers ~1.7× higher heat-extraction efficiency, ~3× longer stable production, a maximum produced-fluid temperature increase of 12.5–19.9 K, and a maximum net thermal-power gain of 8.9–9.4 MW. Even a single-fracture FCLG (SFCLG) outperforms CLG, achieving 2.27× higher efficiency, a 5.5–16.4 K rise in peak produced temperature, and a 2.25–3.6 MW increase in maximum net heat power. These results demonstrate that the FCLG concept and accompanying models can substantially enhance geothermal recovery from abandoned reservoirs, offering a robust framework for high-efficiency energy applications.

Keywords geothermal heat extraction, evolving fractures, closed-loop fractured network