Experimental Study On CO₂ Permeability And Fatigue Mechanical Behavior Of Sandstone After High Temperature Damage

Underground coal gasification technology can transform traditional coal mining into chemical coal mining.The development of the technology is of great help to the situation of"rich in coal,but poor in gas"in China.In addition,underground coal gasification technology has the advantages of high safety and less investment.However,there will be a series of geological problems in the process of underground coal gasification.For example,a large amount of heat will be generated in the process of gasification.The superposition of temperature factors and surrounding rock will produce stress field,temperature field and seepage field in the underground gasifier and its surroundings.These factors have a great impact on the rock mass,which will threaten the safety of gasification engineering and environmental.And the environmental safety is mainly about the leakage of CO₂and other harmful gas.The research on rock mechanics and CO₂ permeability after high temperature damage has important theoretical value and practical significance for underground coal gasification and other engineering problems.In this paper,sandstone is taken as the research object,and the methods of laboratory test and theoretical research are used,the main research contents and conclusions are as follows:(1)The conventional triaxial compression tests of sandstone under different high temperature were carried out,and the stress-strain curves of sandstone specimens under different temperature and confining pressure were obtained.The effects of temperature and confining pressure on the strength parameters,basic deformation parameters and failure characteristics of sandstone specimens were further studied.Combined with the acoustic emission results,the deformation and failure mechanism of sandstone specimens under conventional triaxial compression after different high temperature were revealed.(2)Based on the conventional triaxial compression test results,the uniaxial fatigue tests of sandstone with different amplitude and upper limit stress after high temperature damage were carried out.The effects of different amplitude and upper limit stress on the fatigue life,hysteresis loop,peak strain and failure mode of the specimens were analyzed.The evolution characteristics of elastic modulus,Poisson's ratio and energy in the damage process of the specimen are further studied,and a nonlinear viscoelastic plastic fatigue damage model based on fatigue damage was proposed.(3)The experimental study on CO₂ permeability of sandstone specimens under different high temperature and different stress was carried out,and the variation of CO₂ permeability of sandstone specimens with confining pressure and temperature after different high temperature and different stress was analyzed.The influence of two kinds of damage(high temperature and stress)on the permeability of sandstone was studied,and the mechanism of different high temperature and stress damage on the permeability of sandstone is revealed.This thesis has 82 figures,22 tables and 146 references.