NUMERICAL SIMULATION OF THERMO-HYDRO-MECHANICAL RESPONSE CONSIDERING CLOGGING EFFECT IN GEOTHERMAL EXPLOITATION

Based on the porothermoelastic theory and transient flow field,and considering the clogging caused by fines migration in the fissures of formation,the thermo-poro-elasto-fines migration model of transversely isotropic medium is proposed to consider the coupling characteristics of fines migration,fissure fluid flow,heat transfer,and stress evolution. By using Galerkin weighted residuals and implicit finite difference method,the governing equations of displacement,pore pressure,temperature,and fines concentration are established based on the proposed model,and the finite element procedure is developed to simulate the thermo-hydro-mechanical response of formation under clogging effect during fluid injection/production operations. The existing test data is simulated,and results show the model has a good capacity for predicting the well impedance in the field. The spatiotemporal response of formation to water injection and production is simulated to obtain the influencing mechanism of clogging. Results show that the clogging phenomenon caused by fines migration leads to permeability decline and pore pressure rise surrounding the wellbore. When reservoir temperature is low,the clogging effect could be neglected; higher reservoir temperature makes more fines detach from their original location and enhances the clogging effect,which leads to larger pore pressure surrounding the wellbore and lower exploitation efficiency. By comparing numerical results of reservoir's response with different concentrations of fine particles,permeability decline is found to be more serious for water production,and the clogging effect is weakened when injected water does not contain suspended solids. The conclusions of this study provide theoretical guidance for anti-blocking design in geothermal exploitation.