Coupled THMC modeling on chemical stimulation in fractured geothermal reservoirs

Chemical stimulation, as a soft stimulation method, has been increasingly used in carbonatite geothermal reservoirs, but selecting and designing an optimal scheme of chemical stimulation is still challenging due to lack of robust and reasonable modeling tools. In this study the coupled thermal-hydro-mechanical-chemical (THMC) modeling framework is further developed to simulate chemical stimulation process in carbonatite geothermal reservoirs containing a system of intersecting fractures by considering the nonlinear constitutive models of rock fractures, which reflect the changes in fracture aperture mediated by chemical and mechanical processes. Based on a pilot field test of multi-stage alternate hydraulic and chemical stimulations in the geothermal well D22, Xiong'an New Area, China, the developed modeling framework is verified. The results showed that multi-stage alternate hydraulic and chemical stimulations can efficiently stimulate the carbonatite geothermal reservoirs of low permeability. In addition, a robust optimization approach is proposed to determine the proper human controlled parameters in chemical stimulation including acid concentration, injection rate and total volume of acid solution.