Mining geothermal energy by Electrically Enhanced Geothermal System (EEGS): A new development model of Hot Dry Rock

Hot Dry Rock (HDR) geothermal energy represents an abundant and sustainable energy resource. Among current exploitation methods, Enhanced Geothermal Systems (EGS) are most practical but face challenges including rapid thermal breakthrough, short operational lifespan, and fast thermal decline. To overcome these limitations, we propose an Electrically-Enhanced Geothermal System (EEGS) that actively regulates fluid and heat transport using electro-osmotic flow. A novel Thermo–Hydro–Electric (THE) coupled model is developed, incorporating Darcy flow, electro-osmosis, thermal convection, conduction, and Joule heating, and is validated against analytical benchmarks. Based on temperature evolution and its derivatives at the production well, we identify four sequential stages of thermal response: (I) fracture-dominated accelerated transfer, (II) fracture–matrix exchange-driven deceleration, (III) matrix-dominated accelerated transfer, and (IV) steady conduction. Applying a 200 V DC field opposing the natural flow direction delays thermal breakthrough from 31.7 a to 59.2 a (86.7% delay), and raises the average outlet temperature at 80 a from 379.97 K to 478.53 K (25.95% improvement). Electro-osmotic flow plays the dominant role in transport regulation, while Joule heating remains negligible. Parametric studies show that increasing injection pressure from 79 MPa to 88 MPa advances thermal breakthrough from 66.4 a to 24.5 a (63.2% reduction), while reducing injection temperature from 313.15 K to 288.15 K advances breakthrough from 39.1 a to 28.9 a (26.1% reduction). Economic assessment demonstrates that EEGS achieves significant economic viability with an energy return on investment (EROI) greater than 1, particularly when integrated with curtailed wind or solar power. EEGS provides a non-thermal mechanism to enhance geothermal efficiency and longevity, and can be flexibly integrated with intermittent renewables (wind or solar), enabling hybrid systems with improved thermal stability and sustainable energy output.