Abstract This study characterized and modeled heterogeneous surface wettability in sandstone and investigated the role of spatial heterogeneity and correlation length of surface wettability on relative permeability in a supercritical CO2 (scCO2)-brine-rock system. Understanding the role of wettability heterogeneity on relative permeability is essential to geological CO2 sequestration, oil and gas recovery, and contaminated groundwater remediation. Although numerous studies have attempted to understand the influences of surface wettability, capillary number (Ca), and viscosity ratio, the role of the spatial variation and correlation length of surface wettability on two-phase flow in three-dimensional (3D) porous media has not been unraveled due to the challenges in the measurement and representation of realistic rock surface wettability. In this work, we conducted in-situ measurements of surface contact angle (CA) in a Bentheimer sandstone after CO2 flooding using micro-computed tomography (micro-CT), and found that the pore-scale CA distribution on rock surfaces followed a log-normal distribution associated with a spatial correlation length. Based on the statistical information from CT scanning, a Gaussian random field was used to model CA distributions that had desired standard deviations and spatial correlation lengths, which were then adjusted within a certain range of values for sensitivity analyses to study their combined effects on the two-phase flow in the porous medium using the lattice Boltzmann (LB) method. The LB two-phase flow simulation was accelerated using hybrid, multicore parallel computing to overcome the challenges in simulating multiphase flow in a large 3D domain having 800 × 800 × 600 nodes. The simulation results showed that the surface wettability heterogeneity (i.e., standard deviation of CA) had a lesser effect on the relative permeability of the wetting fluid (water) but a more significant impact on the relative permeability of the non-wetting fluid (scCO2). The Corey model was used to fit the LB-simulated relative permeability curves of water and scCO2 and showed that the variations in the relative permeability curves for both water and scCO2 increased as the standard deviation and spatial correlation length of CA increased. This study illustrated that the assumption of homogeneous surface wettability may cause errors in multiphase flow simulations. The impacts of both the standard deviation and spatial correlation length of CAs should be accounted for. This is the first study that explored the spatial correlation lengths associated with CA distributions on sandstone surfaces and comprehensively investigated the roles of both spatial variation and correlation length of CA on two-phase flow properties in 3D porous media. The optimized LB multiphase flow model was proved a powerful tool to study the interplays and combined effects of these statistical parameters, which had critical applications in numerous natural and engineering processes that involved multiphase flow in porous media.

中文翻译：

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表面润湿性的空间异质性和相关长度对 CO2-水-岩石系统中两相流的作用

摘要 本研究对砂岩中的非均质表面润湿性进行了表征和建模，并研究了空间非均质性和表面润湿性的相关长度对超临界 CO2 (scCO2)-盐水-岩石系统中相对渗透率的作用。了解润湿性异质性对相对渗透率的作用对于地质 CO2 封存、油气回收和受污染的地下水修复至关重要。尽管许多研究试图了解表面润湿性、毛细管数 (Ca) 和粘度比的影响，但表面润湿性的空间变化和相关长度对三维 (3D) 多孔介质中两相流的作用已由于实际岩石表面润湿性的测量和表示方面的挑战，尚未解开。在这项工作中，我们使用显微计算机断层扫描 (micro-CT) 对本特海默砂岩中的表面接触角 (CA) 进行了原位测量，发现岩石表面的孔隙尺度 CA 分布遵循对数-与空间相关长度相关的正态分布。基于 CT 扫描的统计信息，使用高斯随机场对具有所需标准偏差和空间相关长度的 CA 分布进行建模，然后在一定范围内进行调整以进行敏感性分析，以研究它们对两者的综合影响使用晶格 Boltzmann (LB) 方法在多孔介质中的 - 相流。LB 两相流模拟使用混合加速，多核并行计算，以克服在具有 800 × 800 × 600 节点的大型 3D 域中模拟多相流的挑战。模拟结果表明，表面润湿性非均质性（即CA的标准偏差）对润湿流体（水）的相对渗透率影响较小，但对非润湿流体（scCO2）的相对渗透率影响较大. Corey 模型用于拟合 LB 模拟的水和 scCO2 的相对渗透率曲线，结果表明水和 scCO2 的相对渗透率曲线的变化随着 CA 的标准偏差和空间相关长度的增加而增加。这项研究表明，均匀表面润湿性的假设可能会导致多相流模拟中的错误。应该考虑 CA 的标准偏差和空间相关长度的影响。这是第一项探索与砂岩表面 CA 分布相关的空间相关长度的研究，并全面研究了 CA 的空间变化和相关长度对 3D 多孔介质中两相流动特性的作用。优化后的 LB 多相流模型被证明是研究这些统计参数的相互作用和组合效应的有力工具，在涉及多孔介质中多相流的众多自然和工程过程中具有关键应用。这是第一项探索与砂岩表面 CA 分布相关的空间相关长度的研究，并全面研究了 CA 的空间变化和相关长度对 3D 多孔介质中两相流动特性的作用。优化后的 LB 多相流模型被证明是研究这些统计参数的相互作用和组合效应的有力工具，在涉及多孔介质中多相流的众多自然和工程过程中具有关键应用。这是第一项探索与砂岩表面 CA 分布相关的空间相关长度的研究，并全面研究了 CA 的空间变化和相关长度对 3D 多孔介质中两相流动特性的作用。优化后的 LB 多相流模型被证明是研究这些统计参数的相互作用和组合效应的强大工具，在涉及多孔介质中多相流的众多自然和工程过程中具有关键应用。