Study On The Coupling Effect Of THM In Broken Rock Mass During Fault-Mode Geothermal Mining

The process of fault-mode geothermal mining is in the coupling of the three physical fields of "Thermo-hydro-mechanical"(THM)in the broken rock mass,the temperature variation,seepage characteristics,and stress state of the broken rock mass are particularly important for faultmode geothermal mining efficiency,geothermal well stability,and geothermal mining life.In this study,the THM coupling effect of broken rock mass was investigated by theoretical modeling,experimental study,numerical simulation,and engineering simulation,and the temporal-spatial evolution law of its seepage characteristics was obtained and the mechanism of THM coupling was revealed,which provides a theoretical basis for the construction of reservoir,drilling arrangement,and production evaluation of fault mode geothermal mining.The main conclusions are as follows(1)The experimental study of the seepage characteristics of the broken rock mass under the coupling effect of THM was carried out.THM coupling triaxial experimental equipment was designed and developed,the experimental study of THM coupling effects on the broken rock mass under different conditions was carried out,the seepage characteristics of the broken rock mass under THM coupling were obtained,including the rapid variation phase and the smooth variation phase,and the influence of different factors on the seepage characteristics of the broken rock under THM coupling was analyzed.(2)A mathematical model of THM coupling in broken rock mass is established.The model makes the basic assumptions of simplified thermal reservoir calculation according to the characteristics of fault mode geothermal mining,and fully considers the stress state and temperature distribution of the thermal reservoir.The model provides the controlling equations of temperature field,seepage field and stress field of the broken rock mass,and the controlling equations of THM coupled model is given according to the coupling relationship of temperature field,seepage field and stress field.(3)Numerical simulation study of the THM coupling effect of broken rock masses was carried out based on the THM coupling mathematical model,and the model was validated according to the experimental results,and the temporal-spatial evolution of the seepage characteristics of broken rock mass under the effect of THM coupling was obtained,which provides theoretical guidance for fault-mode geothermal mining.(4)The engineering simulation of fault mode geothermal mining in Yangbajing was carried out.The geothermal mining performance under different schemes was obtained,and the production evaluation of different geothermal mining schemes was undertaken to provide a theoretical basis for reasonable mining planning.