中-细粒长石石英砂岩低渗储层在围压循环增减条件下渗透率变化规律的试验研究

二氧化碳(CO_2)地质储存灌注过程大都具有间断性、多期次注入的特点。多期次注入造成储层应力反复积累和消散,储层水平方向的有效应力也将呈现反复加载和卸载效应。通过实验,分析了两个岩石学特征相似的岩心样品在围压循环加、卸载并考虑注入间断期应力消散条件下岩石的渗透率变化规律。试验结果表明,在多次围压加、卸载刺激下渗透率显著下降,降幅可达到20%~40%;间断期应力消散对渗透率的影响很大,实际的注入工程数值模拟计算中应给予充分重视;渗透率变幅在高围压区小,在低围压区域大;根据实验数据构建了黏土矿物含量在10%左右的中-细粒长石石英砂岩低渗储层在多期次围压加、卸载过程的渗透率量化方程,为CO_2地质储存工程多期次注入同类型储层储存潜力评价和CO_2储层监测数据解释提供了理论依据

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.