| Salt rock is an ideal place for underground oil and gas energy storage.The salt cavern reservoirs is generally built in the salt rock layer with a depth of 1 500 m.However,with the rapid development of shallow favorable deposits,the project of salt cavern underground energy storage is developing from shallow(buried depth < 1 500m),to deep(buried depth 1 500?2 500 m)and to ultra-deep(buried depth > 2 500 m).The construction and operation of underground storage also face more complex geological conditions such as high ground stress and high ground temperature.Therefore,it is very important to study the physical and mechanical properties of salt rock under high temperature environment to ensure the safety of storage.Based on the combination of thermodynamic theory and discrete element software,this paper reveals the development mechanism of thermally induced deformation and cracks among grains of salt rock under high temperature environment.The main research contents and achievements are as follows.(1)Based on the theory of rock thermodynamics,the effects of thermal conductivity,specific heat capacity,linear expansion coefficient and thermal diffusivity on thermal damage of rock are studied.Based on the thermal-mechanical coupling equation of rock,the essential model of thermal-mechanical coupling in rock is obtained,which is consistent with the unidirectional coupling in numerical simulation.(2)The microscopic properties and constitutive models of rock thermal damage are analyzed,and the main meso-parameters of simulation are determined.It is found that the rock inhomogeneity and boundary conditions are the key constraints of thermodynamic coupling calculation.By referring to the physical experiment process,a set of reasonable solution steps of high temperature triaxial compression simulation is constructed.(3)A constitutive contact model,which is composed of Burger's model and Linearpbond's model in series,is constructed,and the process of plastic deformation and heat conduction of salt rock is simulated by using particle flow simulation program.By analyzing the stress-strain curve of salt rock,it is found that the lateral strain of salt rock gradually increases in the process of heating up,and the temperature leads to the expansion of rock mass,and the plastic deformation characteristics of salt rock become more obvious with the increase of temperature.(4)The evolution law of damage in salt rock during the heating process and loading stage is analyzed from the perspectives of the failure point of cement,the evolution of force chain and the displacement field,found that the model in central cementation breakdown point along the transverse direction,at the top and bottom model,cementation destroy the oblique extension point,direction and horizontal direction angle of about 45°,halite specimen internal thermal cracking is mainly controlled by tensile stress.The salt rock shows a "drum" failure characteristic,and the azimuthous distribution of the cemented failure points is random,and no obvious macroscopic fracture surface is formed.(5)The thermal damage characteristics of salt rock samples at 20 ?,50 ?,90 ?,120 ? and 150 ? are analyzed by elastic modulus method.The thermal damage values of salt rock samples at 20 ?,50 ?,90 ?,120 ? and 150 ? are respectively 0,0.0860,0.254 3,0.533 0 and 0.781 7,temperature has a significant effect on salt rock.The damage variable index of rock was established based on the damage number of cement.It was found that when the axial strain was (?)=0.07?0.15,the damage variable value of salt rock increases obviously after the ambient temperature is 90 ?. |
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