Numerical Study of the Thermal-Hydraulic-Mechanical Behavior of Fractured Geothermal Reservoirs

Abstract

Fractured geothermal reservoirs are typically sensitive to the thermal and mechanical change induced by cold water injection. It has been observed that the permeability at the cold water injector will be significantly enhanced. The physical process behind this phenomena is that, the cold water injectors lowers the temperature of the reservoir and causes the matrix block to shrink, resulting in an increase of the fracture aperture and the enhancement of fracture permeability. Therefore, it is of great importance to quantify the effect of thermal induced fracture aperture change. In this work, we present a novel correlation of the thermal-induced normal change of fracture aperture. The new correlation is based on the analytical solution of the governing displacement equations. Compared to the existing empirical correlations, the new correlation is semi-analytical and can better reflect the physical processes. We have verified this correlation with respect to refined simulator and implemented this correlation in a fully coupled massively parallel geothermal simulator, THM-EGS. We have used this correlation to study the permeability enhancement effect of a hydraulic connected well pair. The numerical results demonstrates that the permeability near the cold water injector can be enhanced with 2 to 3 order of magnitude.