Study On Mechanical Properties And Permeability Characteristics Of Hot Dry Rock In Gonghe Basin,Qinghai Province

The mechanical and seepage characteristics of dry-hot rock are the key parameters for the efficient development of geothermal energy,involving the whole process of safe drilling,fracturing and long-term heat recovery.With the continuous breakthroughs in the exploration of dry-hot rocks in Gonghe Basin,how to realize the efficient development of dry-hot rocks has gradually become a focus of attention.At present,the study of HDR in Gonghe Basin of Qinghai Province mainly focuses on geological genesis,exploration methods and resource evaluation,and has not systematically studied the mechanical characteristics and seepage characteristics of dry-hot rocks under high temperature conditions.Aiming at the above problems,this paper carries out a systematic experimental study on the physical properties,mechanical parameters and seepage characteristics of HDR in Gonghe Basin of Qinghai Province,tests the evolution law of dry-hot rock fabric,mechanical parameters and seepage characteristics with temperature,establishes the characterization equation of deformation,failure and seepage characteristics of dry-hot rocks,and analyses the influence of the evolution of mechanical and seepage parameters on the thermal efficiency of dry-hot rocks.And the corresponding engineering countermeasures are put forward.Specific research contents are as follows:(1)Study on the Evolution Law of Hot Dry Rock Mechanics CharacteristicsUniaxial and triaxial compression tests and ultrasonic tests were carried out on hot dry rock samples after high temperature heat treatment.According to the stress-strain curve,the deformation characteristics of hot dry rock are analyzed,and the law of mechanical parameters changing with temperature is studied.The acoustic wave test shows that when the treatment temperature is between 300 and 700 ?,the Poisson's ratio of hot dry rock is negative.(2)Establishment of constitutive equation and failure criterion of hot dry rockBy means of XRD,SEM and other experimental methods,the mechanism of mechanical deterioration of dry-hot rocks was analyzed from the aspects of composition and microstructure.The cohesion and internal friction angle of rock are solved by the single-block method and the calculation method,and Mohr-Coulomb strength criterion is revised.Considering the thermal damage and mechanical damage of dry hot rock caused by temperature and load,the constitutive equation of rock under thermal-mechanical coupling is established.(3)Study on seepage characteristics of hot dry rock after high temperature heat treatment.The instantaneous pulse method is used to test and analyze the permeability of hot dry rock after different temperature treatment.The existence conditions of negative Poisson's ratio of hot dry rock are studied,and the possible influence of negative Poisson's ratio on geothermal exploitation is simulated.