Properties Of Fracture Surface In Enhanced Geothermal System Influence On Diversion Capacity

The enhanced geothermal system is a mature dry hot rock geothermal energy development system,that is to say,a large number of fluids are pumped into the target stratum,forming a certain scale of complex fracture network between injection and production wells,enhancing the reconstruction volume and heat transfer area of the thermal reservoir,so as to exploit the underground thermal energy.To study the trend of fracture conductivity under the action of temperature difference and the influence of fracture surface properties on heat transfer law can deepen the understanding of efficient development of enhanced geothermal system.In this paper,based on the testing of the basic properties of granite,the law of the change of the basic thermodynamic parameters with the temperature is obtained;at the same time,the influence of the temperature on the micro and macro mechanical properties of the rock is explored after the low-temperature fluid acts on the high-temperature rock;the experiment of the conductivity of the granite fracture is carried out to study the change law of the conductivity of the shear dislocation fracture with the temperature;the effect of different particle size proppant and sand laying concentration on the The effect of temperature treatment on fracture conductivity is studied by numerical simulation method.The results show that the microcracks increase,the porosity increases from 0.71% to 1.26%,the permeability increases from 8.10×10-18 m2 to 18.47×10-18 m2,the compressive strength decreases from 127.29 MPa to 95.36 MPa,and the elastic modulus decreases from 32.95 GPa to21.25 GPa,Poisson's ratio increased from 0.286 to 0.423.The hardness and elastic modulus of the joint surface decreased with the increase of the treatment temperature,the hardness range is3.78-10.26 GPa,and the elastic modulus range is 87.3-49.8 GPa.The surface profile of the shear fracture has strong randomness.When the roughness difference is small,the fracture is more likely to form a larger conductivity under the condition of large shear dislocation,and the higher the fracture treatment temperature is,the greater the reduction of the conductivity.With the increase of proppant particle size and sufficient proppant concentration,the fracture conductivity can be effectively increased.However,the larger the temperature differences in the heat transfer process,the greater the decrease of conductivity.In the numerical simulation,when the fracture conductivity is low,the outlet temperature of fracture with different conductivity is the same;when the conductivity reaches 30 D·cm,the output temperature decreases with the increase of production time.In the production process,the longer the injection production well spacing,the higher the overall temperature and outlet temperature in the fracture,the smaller the change of temperature field near the production well,and the more heat produced in the reservoir,which is conducive to production.