CO2纯度对咸水层碳封存过程中残余水的影响

CO₂在地下深部咸水含水层的封存过程中，岩石孔隙内形成的残余水对CO₂可注入性、封存量及安全性都有负面影响，因此深入探究各因素影响下残余水的形成演化具有重要意义。文章利用取自鄂尔多斯盆地深部储层的天然岩心，在40℃和8 MPa的实验条件下利用3种纯度的CO₂(99.999%CO₂、75%CO₂+25%N₂以及50%CO₂+25%N₂)进行饱水岩心驱替实验，以探究CO₂纯度对残余水的影响。实验表明，在3种CO₂纯度下的岩心驱替实验中，达到突破点和排水终点所需时间排序均为：99.999%CO₂<75%CO₂+25%N₂<50%CO₂+50%N₂；不可再降残余水饱和度大小排序为：99.999%CO₂<75%CO₂

Effects of CO2 Purity on Residual Water During CarbonSequestration in Deep Saline Aquifers

During the process of CO₂ being injected into deep saline aquifers, residual water formed in rock pore has negative impacts on CO₂ injectability, storage capacity and safety. Therefore, it is important to investigate the formation and evolution of residual water under various influencing factors. In this study, natural rock core taken from the deep reservoirs of the Ordos Basin were used to conduct core-flooding experiments using 3 sets of CO₂ purity (99.999%CO₂, 75%CO₂+25%N2 and 50%CO₂+25%N2) at 40℃ and 8 MPa to investigate the effect of CO₂ purity on residual water. The experimental results show that the order of time required to reach the breakthrough point and the drainage endpoint are, 99.999%CO₂<75%CO₂+25%N2<50%CO₂+50%N2; the order of the irreducible water saturations is: 99999%CO₂<75%CO₂+25%N2<50%CO₂+25%N2. The analysis revealed that changes in CO₂ purity lead to changes of important properties in two-phase floods, such as interfacial tension, wettability, and viscosity ratio. By analyzing the LogCa-LogM displacement stability diagram, the capillary force was determined to be the dominant factor affecting the results of experiments. This study is of great value for predicting residual water saturation under various conditions and evaluating CO₂ sequestration capacity.