| At present,the world energy crisis and environmental problems are becoming more and more serious.Developing new alternative energy sources is an important measure to promote the construction of ecological civilization in China and ensure national energy security.Geothermal resources are highly competitive renewable energy.Studying and developing geothermal resources in hot dry rock（HDR）is an effective way to solve the energy structure problem in China and realize the goal of“carbon peak and carbon neutrality”.Because of the characteristics of dense rock mass,low porosity and low permeability,it is difficult to mine hot dry rock by traditional methods.Enhanced Geothermal System（EGS）is an important means to develop hot dry rock.In this paper,the physical properties of granite are tested,and the mineral composition,porosity and permeability characteristics and thermophysical properties of reservoir are measured.On this basis,the continuous thermal recovery and periodic thermal recovery are numerically simulated by CMG software,and the main conclusions are as follows:（1）The content of plagioclase and quartz in granite reservoir accounts for 77.3%.The average density of rock is 2651.23kg/m3.Porosity ranges from 1.21%～2.36%,with an average porosity of 1.86%.The permeability ranges from 2.9×10-16～9.1×10-16m2,and the average permeability is 0.63m D.The thermal conductivity is in the range of 2.69～2.78W/（m·K）.The average thermal conductivity is 2.74W/（m·K）,and the specific heat capacity ranges from782.86～859.86J/（kg·K）,and the average specific heat capacity is 822.22J/（kg·K）.（2）A numerical model of continuous thermal recovery in hot dry rock fractured reservoir is established,and the sensitivity analysis of well pattern,injection parameters and fracture parameters is carried out respectively,and it is concluded that the scheme of one injection and two productions for horizontal wells is the best.Reducing injection temperature,increasing injection flow,reducing fracture spacing,reducing fracture opening and increasing fracture half-length are beneficial to fully extract thermal energy from rock mass;In this simulation scheme,the optimal results are as follows:injection temperature is 298.15K,injection flow rate is 12kg/s,fracture spacing is 50m,fracture opening is 1.5×10-3m,and fracture half-length is175m.The Grey Relational Analysis method is used to analyze the main control factors affecting the continuous thermal recovery performance.The average temperature of matrix rock,thermal extraction rate and thermal recovery power are taken as evaluation indexes,respectively,and the results are as follows: the injection flow rate > fracture half-length > fracture spacing > fracture opening > injection temperature.Taking the production temperature as the evaluation index,the results are as follows: the fracture half-length > injection flow rate > fracture opening > fracture spacing > injection temperature.（4）A numerical model of periodic thermal recovery in hot dry rock fractured reservoir is established,and it is concluded that compared with continuous thermal recovery,the production mode of periodic thermal recovery can increase the production temperature of fluid and prolong the production life of the system.The sensitivity analysis of the influence of shut-in time,injection flow rate and fracture spacing on reservoir thermal recovery capacity is carried out respectively.Prolonging shut-in time,increasing injection flow rate and increasing fracture spacing are beneficial to reservoir thermal recovery. |
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