低渗透储层岩石覆压实验变形特征分析

对于低渗透储层岩石而言，基于岩石受力变化后发生线弹性变形的假设与实验结果并不相符。为此，采用CMS300覆压测试、岩石力学性质测试、压汞以及铸体薄片观察等实验手段对低渗透储层岩石覆压变形特征进行分析，结果发现实验岩样在应力增大的整个过程中发生的是软塑性变形→弹性变形→塑性变形过程。低渗透岩石在覆压实验中表现出的强应力敏感性是由其变形特征决定的，岩石在覆压增大的初始阶段发生微量软塑性变形是造成渗透率大幅下降的主要原因，其与低渗透岩石的泥质及胶结物含量较高、孔喉通道狭窄有关。基于实验研究结果，定义了新的岩石应力敏感系数来表达渗透率与有效覆压的关系，与实验数据有更好的相关性,并且能够方便地将任意常规岩样渗透率转换成储层条件下的渗透率，具有实际的工程应用价值。

The deformation characteristics of low permeability reservoir rocks under confining pressure

For low permeability reservoir rocks, the hypothesis that linear poroelastic deformation occurs when rocks are compressed does not coincide with the laboratory findings. For this reason, various experimental methods, including the CMS300 test under confining pressure, rock mechanics test, mercury injection and cast thin section analysis, were adopted to study the deformation characteristics of low permeability reservoir rocks under confining pressure. The experimental results show that the rock sample has first experienced  soft plastic deformation, and then elastic deformation, and finally plastic deformation as the stress increases. The strong stress sensitivity of low permeability rock samples in the experiment under confining pressure is determined by their deformation characteristics. Subtle soft plastic deformation of rocks at the initial stage of confining pressure increasing is the main cause of significant decrease of permeability, and it is related with the relatively high contents of shale and cements as well as narrow pore throat of low permeability rocks. Based on the experimental results, a new coefficient of stress sensitiveness is defined to express the relationships between the permeability and the effective confining pressure. It has better correlativity with the experimental data, and can be used to conveniently convert the permeability of conventional rock samples into the permeability under reservoir conditions.