盐穴储气库溶腔收缩规律分析

THE CREEP DEFORMATION RULE OF GAS STORAGE SALT CAVERN

盐穴储气库在运行过程中溶腔周围的盐层受到地层压力和溶腔内压的多重作用而产生应力变化。由于盐层具有蠕变特性,并且溶腔内压力始终小于周围岩层的地层压力,因此溶腔周围盐层会产生指向溶腔内部的位移而导致溶腔收缩,从而引发储气库单腔库容和工作气量的变化。溶腔的收缩可以通过盐层蠕变测试结合数值模拟进行预测。通过对国内某盐穴储气库实际岩石力学参数测定和溶腔运行模拟预测发现,溶腔建成初期有一个短暂的快速收敛阶段,后期收敛速度较为平稳并有逐步减缓的趋势。运行10年,溶腔的体积缩小逾8%,对应的储气库库容和工作气量也将减少8%以上。因此在盐穴储气库运行的初期,必须密切注意溶腔蠕变,制定合理的运行参数,确保溶腔快速收缩阶段的溶腔稳定。在中后期必须新建溶腔,以弥补因溶腔收缩而减少的库容量及工作气量。

During the operation of the salt cavern gas storage, the salt bed around the salt cavern will generate variation of stresses because of strata pressure and internal pressures of the salt caverns. As the internal pressure of the salt cavern is always poorer than the strata pressure and the plastic deformation will occur on the salt bed under high pressure, accordingly, the surrounding salt bed will generate displacement toward the inner salt cavern whereby the salt cavern will be converged. Therefore, the single cavern storage capacity and the working gas volume will be changed which will reduce the operational efficiency of the salt cavern. The salt cavern convergence and the creep deformation of the salt bed have close relationship. Based on the measurement by the rock mechanics, this study analyzed the creep deformation characteristics of the salt bed and accordingly set up the constitutive equation. The creep deformation of the salt bed in various part of the salt cavern at different stages with different operational status can be simulated through the constitutive equation and establishment of the three-dimensional model for the salt cavern, thereby to predict the convergence rule of the whole salt cavern. According to the findings in the salt cavern operation simulation, at the early stage after the salt carven were built, there was a short-lived rapid convergence stage, while at the late stage, the convergence pace was relatively stable and gradually slowed down. Therefore, at the early operational stage of the salt cavern gas storage, we should closely follow the creep deformation of the salt cavern and formulate reasonable parameters to guarantee the safe and efficient operation of the salt cavern; while at the middle- and late-stage, we should rebuild salt cavern for making up the storage capacity and working gas reduced by the convergence of salt cavern.