蠕变作用下层状盐岩界面剪切应力变化规律研究

层状盐岩储气库在长期运行期间,盐岩层与泥岩夹层两种不同岩石材料会因较大的蠕变差异引起变形不协调,在交界面产生剪切应力导致界面滑移破损,使油气沿着界面破损通道泄漏。结合我国在层状盐岩地质构造中建设能源储库的实际情况,通过对湖北云应地区层状盐岩中的盐岩和泥岩夹层的三轴蠕变试验表明,盐岩蠕变率比泥岩蠕变率至少大一个数量级。建立蠕变本构模型,对储库长期运行期内层状盐岩界面剪切应力的分布和变化规律进行数值分析,并讨论了盐岩稳态蠕变率不同时,界面层间剪切应力的变化情况。研究结果表明,界面层间剪切应力集中分布在靠近腔体的小段范围内,其后层间剪切应力迅速降低,且随着蠕变时间的增加,层间剪切应力增加的越来越快;盐岩的蠕变特性越好,层间剪切应力越大,当界面剪切应力达到界面抗剪强度时,就会发生破坏。蠕变试验和数值模拟结果,对于层状盐岩渗漏稳定性和密闭性研究具有重要指导意义。

Interface Shear Stress Distribution of Bedded Salt Rock Considering Rheology Effect

During the long term operation of gas storage in underground bedded salt carven, the big difference in creep rate between salt rock and mudstone interlayer due to their different physical properties, leading to inconsistency of deformation and the sliding damage occurs at the interface due to shear stress, which will results in gas leakage along the damaged zone. Considering the construction of storage in salt rock under current geological conditions in China, a series of triaxial creep experiments concerning the tightness of the salt cavern were carried out in Yunying the mine in Jianghan Oilfield. The results show that the creep rate of salt rock is one-magnitude-order larger than that of mudstone. Based on proposed creep constitutive model, using 3-D numerical simulation, the evolvement of shear stress along the interface is simulated under different creep rates. From the results it is demonstrated that the shear stress of interlayer is mainly located in certain range near the gas cavern, and it becomes smaller and smaller quickly with increasing distance. And also with increase of creep time, interlayer shear stress increases soon. It is found that bigger steady creep rate of salt rock induces bigger shear stress; therefore, the shear failure induced by creep is closely related to cavern tightness and which should be paid much attention to. The results illustrate that the creep experiments and numerical simulation have great reference value and practical significance for the research of underground storage construction project.