THM Coupling Model Of Fractured Reservoir In Hot Dry Rock Mining And Its Application

As a new type of renewable energy,hot dry rock can effectively solve the problem of energy shortage and environmental pollution.China has very rich hot dry rock resources,but the conditions are relatively harsh.It is difficult to carry out physical experiments during the research process,so theoretical research and numerical simulation have become effective research methods accepted by scholars.First,this paper proposes a new type of horizontal-layered Enhanced Geothermal System(EGS),based on the equivalent medium model thermal-fluid-solid three-field coupling theory and the geothermal data of the geothermal field in Gonghe Basin,China.And through three aspects of flow field,temperature field and heat recovery effect,this system is compared with the traditional double shaft enhanced geothermal system.It is found that under the conditions of this paper,the horizontal-layered EGS heat recovery effect is significantly better than the traditional double shaft EGS.Although the average production temperature of the double-shaft EGS is higher than that of the horizontal-layered EGS in the decay stage,for the thermal output power,the horizontally-layered EGS is 6.10-12.25 MW,which is 1.36-1.67 times that of the double-shaft EGS.In addition,the heat recovery rate of horizontal-stratified EGS is nearly 7%higher than that of double-shaft EGS,which has higher economic benefits.Secondly,the paper analyzes the influence of artificially controllable factors(pressure difference between injection and production wells,well spacing and injection fluid temperature)on heat recovery in horizontal-layered EGS.In general,the heat output and heat recovery rate are proportional to the pressure difference and well spacing,and inversely proportional to the temperature of the injected fluid.Specifically,among the factors that affect thermal output power,the effect of pressure difference is the largest,and the effect of well spacing is the second,and the factor that has the least effect is the temperature of the injected fluid;among the factors that affect the thermal recovery rate,the pressure difference and the well spacing have the same effect,and the effect of the injection fluid temperature on the thermal recovery rate is negligible.For heat recovery radius:Both the increase in pressure difference and well spacing will increase the heat recovery radius,but the former's increasing effect will weaken as the pressure difference increases,while the latter's increasing effect will increase with time and the increase;the effect of the temperature of the heating fluid on the heating radius is negligible.Finally,based on the matrix-fracture dual-medium model and a heat recovery cycle in horizontal-layered EGS as a research object,a fracture system in which the main fractures of the injection and production wells and the existing natural fractures coexist is established.Effects of natural fissures,angles between main fissures and natural fissures,and main fissure permeability on heat extraction process.The results show that:(1)For natural fractures,the natural fractures connected to the main fracture play a role in expanding the fluid migration area,while the natural fractures not connected to the main fracture only play a role in water storage;the natural fractures affect the output thermal power Larger,but the impact on the average production temperature and heat recovery rate is relatively small.(2)For the angle between the main fracture and the natural fracture,the angle is inversely proportional to the permeability between the two wells;if you want to improve the heat recovery rate and the average production temperature in the project,you can increase the angle within 30°~60°of the angle between the fractures.(3)Regarding the permeability of the main fracture,appropriately reducing the permeability of the main fracture can obtain a long-term stable production well temperature;under the conditions of this paper,the permeability of the main fracture is within the range of 5×10~-1414 m~2~2×10~-1313 m~2,which increases the economic efficiency of heat recovery.