Heat extraction of enhanced geothermal system: Impacts of fracture topological complexities

Highly efficient stimulating fracture network is crucial for the utilization and operation of enhanced geothermal systems, in which involved heat transfer and fluid flow process highly depends on fracture topological complexities. However, as more realistic morphologies, non-planar fractures are always ignored in previous reservoir simulations and its influence mechanism on heat extraction is not fully understood yet. Hence, this study aims to reveal the impacts of non-planar fractures on heat and mass transfer in enhanced geothermal system. Based on thermal–hydraulic–mechanical fully coupling and finite element methods, we comprehensively investigated how non-planar structure (fracture and fault), continuity and fracture networks affected production temperature, mass flow rate and power generation rate. Results indicate that non-planar and continuous fracture morphology greatly reduce flow resistance and fluid leakage. Over 15% of fluid leakage recycling and 10 MW heat output improved in non-planar fracture models. Faults are noted as effective flow channels and contribute 5∼8% of production flow rate and heat output. Whereas, branch fractures and complex fracture network do not always benefit to heat extraction but enlarging fluid leakage, which is related to intersection angle, fracture number and connectivity. A comprehensive evaluation of fracture morphology and implications are done in this study.