Numerical simulation of the thermo-hydro-chemical coupling in enhanced geothermal systems: Impact of SiO2 dissolution/precipitation in matrix and fractures.

The hydraulic properties of reservoir matrix and fractures, as well as the production performance of enhanced geothermal systems, can be significantly affected by chemical dissolution and precipitation. Therefore, chemical reaction effects must be considered when exploiting dry hot rock resources. To investigate the impact of chemical effects, this study incorporates the dissolution/precipitation process of silica in the reservoir matrix and fractures and establishes a thermo-hydro-chemical coupling dual-well model that includes a main fracture and multiple secondary fractures. Results indicate that under-saturation injections increase the mechanical aperture of the main fracture by up to 0.066 mm and permeability by up to 217.3 % over a 30-year production period. Oversaturation injections decrease the mechanical aperture by up to 0.035 mm and permeability by up to 66.1 %. Reservoir matrix permeability exhibits a noticeable zonal distribution, with a maximum increase of 22.6 % in the under-saturation injection and a maximum decrease of 4.1 % in the saturation injection over a 30-year production period. Chemical reactions have a significant impact on the average production pressure. Neglecting chemical reactions in the matrix may result in overestimation or underestimation of changes in production pressure. These results provide a reference for the sustainable production of EGS in the long term. • A thermo-hydro-chemical (THC) coupled model is established for the development of enhanced geothermal system. • THC coupled process is simulated in a double well production model with a primary fracture and multiple secondary fractures. • The permeability evolution of both reservoir matrix and fractures affected by silica dissolution/precipitation is analyzed. • The impact of chemical effects on geothermal recovery efficiency is predicted. [ABSTRACT FROM AUTHOR]