Long-term CO2 geological storages are mostly injected in a process with the characteristics of dis-continuity in multiple injection stages. Intermittent injections cause reservoir stress to accumulate and dissi-pate repeatedly, and horizontal effective stress in the reservoir also appears repeated loading and unloadingeffect. Through experiment,the permeability of two rock samples with similar petrological features were ana-lyzed under the circulatory loading and unloading conditions of confining pressure,and in consideration ofstress dissipation during injection gap period. The experimental results show that the permeability are de-clined significantly with the declines ranging in 20% ~ 40%,under the repeated loading and unloading con-dition of confining pressure. The change of permeability is smaller in high confining pressure area, whilebigger in low confining pressure area. The stress dissipation in injection gap period has much effect on therock permeability, and full attention should be given to the numerical simulation of actual injection engi-neering. Based on the experimental data,the permeability quantitative equations in different loading and un-loading stage of confining pressure have been built for the medium-fine-grained feldspar-quartz sand-stone with about 10% clay mineral content. The result is helpful to evaluate the potential of reservoir stor-age and to interpret the monitoring data of CO_2 geological storage project with multi-period injection.
Journal of Hydraulic Engineering
cyclic loading and unloading