真三轴应力下液氮注入煤样损伤特性模拟研究OA

In order to clarify the internal damage evolution law of liquid nitrogen injection into coal samples under real in-situ stress,a three-dimensional coupling model of thermal-hydraulic-mechanical-damage of heterogeneous coal was established by COMSOL Multiphysics numerical simulation software.The temperature,permeability and damage variation of coal samples during injection were analyzed.Considering such factors as minimum principal stress and injection pressure,the mechanism of liquid nitrogen injection on coal sample damage under true triaxial stress was discussed.The results show that:After 20 min of liquid nitrogen injection,the low temperature liquid nitrogen is close to the outer surface of the coal sample,and the fracture network is formed inside the coal sample,and the permea-bility is 2 times higher than that without injection.As the minimum principal stress increases from 2 MPa to 5 MPa,the final damage of coal body shows a linear growth trend.Under the condition of 5 MPa stress,the final damage degree of coal sample is 84.1％.When the injection pressure increases from 0.40 MPa to 0.55 MPa,the final damage degree of the coal sample increases significantly to 92.3％,and the damage growth rate is the most significant in the pressure range of 0.45～0.50 MPa,reaching 24.1％.Under the influence of three-dimensional unequal stress,the internal low-temperature region of the coal sample shows obvious directional selectivity,and the damage of the coal sample preferentially develops along the direction.The research results reveal the dynamic evolution law of coal sample dam-age under the multi-field coupling of thermal-hydraulic-mechanical-damage,which can provide a theoret-ical basis for the application of liquid nitrogen fracturing technology in coal mine.