Experimental study on the variation of permeability of medium-fine feldspar-quartz sandstone low-permeability reservoir under the circulatory increasing or reducing conditions of confining pressure

Long-term CO2 geological storages are mostly injected in a process with the characteristics of discontinuity in multiple injection stages. Intermittent injections cause reservoir stress to accumulate and dissipate repeatedly, and horizontal effective stress in the reservoir also appears repeated loading and unloading effect. Through experiment,the permeability of two rock samples with similar petrological features were analyzed under the circulatory loading and unloading conditions of confining pressure, and in consideration of stress dissipation during injection gap period. The experimental results show that the permeability are declined significantly with the declines ranging in 20% ~ 40%,under the repeated loading and unloading condition of confining pressure. The change of permeability is smaller in high confining pressure area, while bigger in low confining pressure area. The stress dissipation in injection gap period has much effect on the rock permeability, and full attention should be given to the numerical simulation of actual injection engineering. Based on the experimental data,the permeability quantitative equations in different loading and unloading stage of confining pressure have been built for the medium-fine-grained feldspar-quartz sandstone with about 10% clay mineral content. The result is helpful to evaluate the potential of reservoir storage and to interpret the monitoring data of CO2 geological storage project with multi-period injection. © 2016, China Water Power Press. All right reserved.