地下盐穴储气库盐岩热损伤机理

Thermal damage mechanism of salt rock in underground salt cavern gas storage

基于变质量热力学原理,建立盐穴储气库注采过程中的工程热力学分析数学模型,给出了单个注气和采气过程中温度和压力随时间变化的解析解,作为数值模拟的边界条件。根据金坛储气库的基本数据和盐岩实验研究参数,利用COMSOL Multiphysics有限元软件建立单腔盐穴注采过程的温度—应力耦合模型,模拟恒定注采速率下盐腔围岩的拉伸损伤、剪切损伤和膨胀损伤分布情况,研究夹层和热应力对围岩损伤的影响。基于热应力理论,结合模拟结果分析盐穴储气库注、采气过程中围岩的热损伤机理。模拟结果表明:在热应力存在的情况下,夹层的存在促进了围岩损伤的产生,无夹层时围岩无损伤发生,有夹层时围岩存在损伤;注气过程和采气过程的损伤发生位置存在差别:注气过程损伤多发生在夹层附近的盐岩中,采气过程损伤多发生在夹层中;膨胀损伤的范围最广,且损伤范围覆盖了前2种损伤,因此实际生产过程中推荐使用膨胀损伤判据,损伤评价结果更为保守。

Based on variable mass thermodynamic principle,a mathematical model of thermal analysis is proposed for gas injection and production process in salt cavern gas storage.Then an analytical solution is provided for temperature and pressure variation with time during single gas injection and production process,which can be set as boundary conditions of numerical simulation.According to the basic data of Jintan underground gas storage and the rock salt properties acquired from experiments,a thermal-mechanical coupling model is established for gas injection and recovery process in one single salt cavern by using the finite element software COMSOL Multiphysics FEM.Through simulating the distribution of tensile damage,shear damage and expansion damage of the surrounding rock in salt cavern under constant injection-production rate,this study investigates the influence of interlayer and thermal stress on the damage of surrounding rock.Based on the thermal stress theory in combination with simulation results,this study analyzes the thermal damage mechanism of surrounding rock during the injection-production process in salt cavern gas storage.The simulation results indicate that in the presence of thermal stress,the interlayer can promote the damage of surrounding rock.There is no damage in the surrounding rock in case of no interlayer,while the surrounding rock is damaged when the interlayer exists.There is a difference in the location of damage during gas injection and production process.The damage during gas injection process often occurs in the salt rock near the interlayer,while the damage during gas production process often occurs in the interlayer.The expansion damage is distributed most widely,and the damage range covers the first two kinds of damage.Therefore,it is recommended to use the criterion of expansion damage in the actual production process,and the results of damage evaluation are more conservative.