A Three-dimensional Coupled Thermo-hydro Model for Enhanced Geothermal Systems

A three-dimensional numerical model of coupled fluid flow and heat transfer in EGS reservoir is investigated. The model considers a single uniform fracture surrounded by a three dimensional low permeable rock matrix. The flow is imposed on a fracture plane, consisting of a doublet system. The primary objectives of this paper are to analyze the effects of injection temperature and mass flow rates on heat extraction performances. The study results showed that for lower injection temperature heat extraction rates from the reservoir are higher. In case of higher injection mass flow rate, energy output increased significantly. However, after thermal breakthrough the energy output drops are seen faster in comparison of lower mass injection case. The faster energy drop with the time are result of the slower heat conduction inside the low permeable rock matrix perpendicular to the fracture. The present model neglected the fracture aperture evolution even though transmissivity reduction is observed. The transmissivity reduction is the results of flow resistance. The flow resistance inside the fracture is increased due to the non-laminar flow and cooling. The combined effect leads to rise the flow impendence of the reservoir. These effects are more for the higher mass at the lower injection temperature.