| Energy is one of the main driving forces for the development of the human society and the economy.With the development of the world's science and technology,the energy crisis is becoming more and more obvious.To ensure energy security,the development of new energy resources has become the main solution to the current energy problem.Hot dry rock(HDR)resource is one of high temperature geothermal resources underground,but due to the dry hot rock is buried deep,the high crustal stress and high the temperature,so that the rock mass is dense,natural cracks are small,and the permeability is low,the development technology requirements of HDR are higher.Enhanced Geothermal Power(EGS)is an artificial system that extracts heat from low-permeability rock by reservoir stimulation technology.There are also many problems to be solved,achieving high permeability,high heat conversion rate and the reduction of fracturing fluid leakage rate,etc.,so that reducing development costs,reducing environmental impact and improving utilization,promoting the development and utilization of dry hot rock resources and the commercialization process of enhanced geothermal systems.In this paper,the key problems of reservoir stimulation in the development of enhanced geothermal system are studied by experimental research.The true triaxial hydraulic fracturing simulation test of the Indosinian large-size granite in the Gonghe Basin is carried out,and the occurrence and development of hydraulic fissures are studied.After data collation and literature study,we have known the Republic Basin has the conditions for geothermal formation in the evolution causes and geological structures,and has heat sources,reservoirs and caprocks.It has abundant geothermal resources,high geothermal gradient.So Gonghe Basin has great potential for development.After the experimental research,the following conclusions are drawn:(1)Confining pressure has a controlling effect on crack development.The main fracture direction is always on the normal surface of the minimum principal stress,and the larger the confining pressure,the slower the fracture expansion rate,the smaller the number of small fractures,and the direction of the geostress.Mastery,in the fracturing,can control the direction of the formation of the fracture,thus forming a network of mutual fractures.Secondly,the larger the confining pressure,the more the fracturing fluid accumulates in the crack,and the larger the crack width,the more favorable the fracturing fluid enters and the heat exchange efficiency.(2)The formation of cracks begins at the bottom of the total borehole.The main cracks and natural cracks formed first have an inhibitory effect on the subsequent cracks.The reason is that after the cracks are formed,the fracturing fluid enters in a large amount,and the pressure at the bottom of the pores is dispersed into the cracks.Secondly,the hydraulic fracture patterns of the rock samples are similar,but the direction of the crack propagation varies due to the direction of the axial stress.(3)The permeability of the hydraulic fracture of the sample can be calculated and evaluated by a certain method.Through the theoretical basis of hydraulics and hydrogeology,the permeability of the sample after the test is calculated,and the permeability of most of the EGS development is compared.The artificial crack formed in this test is of a flow-directing meaning.(4)For the field fracturing project,in the case of mastering the development law of the fracture,by combining the existing fracture,the magnitude of the ground stress and the hydrogeological parameters,the interconnected fracture network can be formed more effectively. |
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