Field scale numerical modeling of heat extraction in geothermal reservoir based on fracture network creation with supercritical CO2 as working fluid

Abstract

In geothermal reservoirs, the typically low natural permeability needs to be stimulated for an efficient heat extraction. In this work, the stimulation of heat extraction as well as the associated CO2 sequestration in geothermal reservoirs is studied, based upon supercritical CO2-EGS (enhanced geothermal system) concept in a 3D continuum anisotropic damage-permeability model under thermal–hydraulic–mechanical framework. The developed approach has been applied into the planned Dikili EGS project in Turkey. The simulation results show that a fracture network with a stimulated reservoir volume of 8.71 × 107 m3 is created by injecting 90,000 kg CO2 in 250 h. A priority channel with high gas saturation in the fracture network is formed during heat extraction because of the viscosity difference between CO2 and water. In general, for both water and CO2 injection, the driven pressure and average thermal capacity shows a positive correlation with injection rate, while the eventual produced temperature shows a negative correlation with injection rate. In comparison with water as working fluid for heat extraction, CO2 owns some benefits like low driven pressure and high eventual produced temperature. Besides, a positive correlation between sequestrated CO2 mass and injection rate is observed. Approximately 950, 000 tons of CO2 are geologically sequestrated under injection rate of 100 kg/s over 30 years of production period.