Abstract This study investigates the effect of heterogeneity on CO2–brine two-phase flow behavior and capillary trapping at the field scale. A model based on macroscopic invasion percolation is developed to simulate CO2 migration and trapping in strongly heterogeneous systems with bimodal permeability distributions. Stochastic simulations are performed on heterogeneous permeability fields generated by considering both transition probability based lithofacies distribution and multi-Gaussian random fields, representative of characteristics often encountered in relevant sedimentary basins. The heterogeneity cases of different lithofacies proportions are designed such that they share the same ensemble mean of upscaled permeability over the simulation domain. We find that the CO2 spreading and trapping is strongly influenced by the heterogeneity. The ensemble means of sweep efficiency and domain-average CO2 saturation after primary drainage show a slight decrease with decreasing sandstone proportion p1 from 1.0 to 0.6 but a much steeper decline when p1 further decreases to 0.4. The upscaled two-phase flow properties such as the relative permeabilities are also influenced by the lithofacies proportion. Residual or capillary trapping and its uncertainty is shown to be dependent on the heterogeneity and the choice of trapping models. Our findings have broad implications within the context of CO2 sequestration, as the gas spreading and entrapment are the fundamental processes leading to long-term storage security.

中文翻译：

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CO2地质封存过程中双峰非均质介质中的气体运移和残余捕集

摘要 本研究在现场研究了非均质性对 CO2-盐水两相流动行为和毛细管捕集的影响。开发了一种基于宏观入侵渗透的模型，以模拟具有双峰渗透率分布的强非均质系统中的 CO2 迁移和捕获。对通过考虑基于过渡概率的岩相分布和多高斯随机场产生的非均质渗透率场进行随机模拟，这些场代表了相关沉积盆地中经常遇到的特征。不同岩相比例的非均质性情况被设计为在模拟域上共享相同的放大渗透率集合平均值。我们发现 CO2 的扩散和捕获受到异质性的强烈影响。随着砂岩比例 p1 从 1.0 降低到 0.6，一次排水后波及效率和域平均 CO2 饱和度的集合平均值显示出略有下降，但当 p1 进一步降低到 0.4 时下降幅度更大。相对渗透率等放大后的两相流特性也受到岩相比例的影响。残留或毛细管捕集及其不确定性取决于异质性和捕集模型的选择。我们的发现在 CO2 封存的背景下具有广泛的意义，因为气体扩散和截留是导致长期储存安全的基本过程。6 但当 p1 进一步下降到 0.4 时下降幅度更大。相对渗透率等放大后的两相流特性也受到岩相比例的影响。残留或毛细管捕集及其不确定性取决于异质性和捕集模型的选择。我们的发现在 CO2 封存的背景下具有广泛的意义，因为气体扩散和截留是导致长期储存安全的基本过程。6 但当 p1 进一步下降到 0.4 时下降幅度更大。相对渗透率等放大后的两相流特性也受到岩相比例的影响。残留或毛细管捕集及其不确定性取决于异质性和捕集模型的选择。我们的发现在 CO2 封存的背景下具有广泛的意义，因为气体扩散和截留是导致长期储存安全的基本过程。