Coupled THMC Modeling on Acidizing Process in Fractured Carbonatite Geothermal Reservoirs
Haoran XU1+, Zhihong ZHAO2#, Feng MA3, Guihong LIU1, Guiling WANG3
1Department of Civil Engineering, Tsinghua University, China, 2Tsinghua University, China, 3Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, China

Chemical stimulation, as a soft stimulation method, has been increasingly used in geothermal reservoirs because of its low risk of induced seismicity. A nonreactive fluid is first injected to connect natural fractures with hydraulic pressure, followed by injecting acid to etch fracture walls. The main aim of this study is to further develop a fully coupled thermo-hydro-mechanical-chemical (THMC) modeling framework for chemical stimulation in carbonatite geothermal reservoirs containing a system of intersecting fractures. A nonlinear constitutive models for rock fractures are included in the present modeling framework. The developed modeling framework is verified using a case study of chemical stimulation in the geothermal well, Xiongan New Area, China. The simulation results indicate that the injection of high viscosity nonreactive fluid significantly increased the apertures of pre-existing fractures and resulted in some tiny shear sliding of fractures within 10 meters from the wellbore. There was no obvious fault slip induced, which was consistent with the results from microseismic monitoring. Fractures with high initial aperture and strick parallel to the direction of maximum horizontal principal stress are easier to be stimulated. The sensitivity analysis of acid concentration, injection rate, perforation depth and direction are also carried out to provide an optimal solution for local acidizing acid fracturing design.