Simulation Analysis Of Deformation And Failure Law Of Dry Hot Rock Wellbore Containing Structural Surface

Dry hot rock resources are abundant in china,and dry hot rock energy is more stable than solar energy and wind energy,and has little impact on the environment.Dry hot rock clean energy generation is the trend of the future energy revolution.Most of the dry hot rocks occur in the high temperature and high pressure and structural surface development strata.The physical and mechanical properties of the rock mass have changed greatly under the coupling of multiple physical fields,which causes the well wall to be unstable and also increased during the drilling process.It is difficult to maintain the stability of dry hot rock shaft wall under the coupling of multiphysics.Therefore,it is of great theoretical and engineering significance to study the stability of shaft wall with dry surface of structural hot surface under multi-physics coupling.In order to better develop dry hot rock,this paper takes the construction of national dry hot rock development demonstration base as the starting point,combines the geological data obtained from the exploration results of each dry hot rock target area,characterizes the physical and mechanical properties of dry hot rock,and then constructs geology.Based on the theory of heat transfer,elastoplastic mechanics and rock mechanics in the model,and establishes the thermoelastic and thermoviscoelastic thermodynamic coupling equations,respectively,using Mohr-Coulomb(M-C)and Drucker-Prager(D-P)strength criteria.The three-dimensional numerical simulation of COMSOL software is carried out to study the deformation and failure law of dry heat rock shaft underthe influence of different temperature,maximum horizontal stress,caliper,structural surface thickness,structural plane inclination and number of cracks in the drilling process,and then determine the damage area of the surrounding rock of the dry hot rock wellbore.(1)Analysis of geological structure characteristics and physical and mechanical properties of dry-hot rocks,the following conclusions are obtained:1)Most of the dry-hot rocks are located in the uplift faults,subsidence basins and areas with frequent magmatic activities.Recent tectonic movements,intrusion by magma,and good The sedimentary caprock.2)The thermophysical parameters of dry hot rock vary greatly from 150°C to 400°C,which is related to the interstitial fissure structure,interlaminar water and structural water removal and mineral decomposition.(2)According to the indoor experimental geological model,the geometrical mechanical model is established.The dry hot rock is regarded as the thermal elastoplastic body and the hot viscoelastic body respectively.The corresponding thermal coupling mathematical model is established.Respectively,the M-C strength criterion is used to judge the well in the elastoplastic model.Whether the wall is unstable,and the D-P strength criterion is used to judge whether the well wall is unstable in the viscoelastic model.The numerical simulation is carried out by using COMSOL software to study the deformation and failure law of the dry heat rock well under different conditions,and the following conclusions are obtained: 1)In the elastoplasticity or viscoelastic model,the temperature field of the dry heat rock wall shows symmetry,similarity,limitation,vectority and difference.2)In the elastoplastic or viscoelastic models,the stress field of the dry hot rock wellbore also has the distribution law of symmetry,consistency,range and difference.The radial stress and tangential stress of the wellbore do not conform to the linear elastic solution.The maximum difference between the two is not at the well wall.It can be seen that the failure position of the wellbore is not necessarily at the well wall,and maybe some distance from the well wall.Location.3)In the elastoplastic model,the well wall is preferentially destroyed at the structural plane;in the viscoelastic model,the specific damage of the dry heat rock wall is related to the boundary conditions of the rock.4)In the elastoplastic model,the lower the temperature,the smaller the maximum horizontal stress,the smaller the thickness of the structural surface,and the smaller the number of cracks,the better the stability of the well wall,and the viscoelasticity.In the model,the lower the temperature,the smaller the maximum horizontal stress,the smaller the thickness of the structural surface,the larger the inclination angle of the structural plane,the more favorable the stability of the borehole wall;however,there is an optimal diameter to wellbore stability in both models.Most beneficial.5)In the viscoelastic model,the creep process of the dry heat rock wall only experienced two stages of initial creep and constant velocity creep,and there was no accelerated creep phase.(3)Studying the damage of surrounding rock of the shaft with dry heat in the structure with thermal coupling,the following conclusions are obtained: 1)From the perspective of the damage area,regardless of the elastoplastic or viscoelastic model,the surrounding rock damage of the dry hot rock well is around the well wall or at the structural plane,the damage range of the structural surface is always larger than that of granite.The elastoplastic model simulation results are more in line with the actual engineering experience at 150°C~250°C.The viscoelastic model is more suitable when the temperature is between 250°C and 400°C.2)From the perspective of damage radius,the temperature,caliper,structural plane inclination and number of cracks have a great influence on the damage radius of dry heat rock wellbore.3)From the ratio of damage volume,the temperature,caliper and number of cracks are the main factors causing the difference of wellbore damage in dry hot rock in elastoplastic and viscoelastic models.