Abstract

Wettability is one of the critical parameters affecting multiphase flow in porous media. The wettability is determined by the affinity of fluids to the rock surface, which varies due to factors such as mineral heterogeneity, roughness, ageing, and pore-space geometry. It is well known that wettability varies spatially in natural rocks, and it is still generally considered a constant parameter in pore-scale simulation studies. The accuracy of pore-scale simulation of multiphase flow in porous media is undermined by such inadequate wettability models. The advent of in situ visualization techniques, e.g. X-ray imaging and microtomography, enables us to characterize the spatial distribution of wetting more accurately. There are several approaches for such characterization. Most include the construction of a meshed surface of the interface surfaces in a segmented X-ray image and are known to have significant errors arising from insufficient resolution and surface-smoothing algorithms. This work presents a novel approach for spatial determination of wetting properties using local lattice-Boltzmann simulations. The scheme is computationally efficient as the segmented X-ray image is divided into subdomains before conducting the lattice-Boltzmann simulations, enabling fast simulations. To test the proposed method, it was applied to two synthetic cases with known wettability and three datasets of imaged fluid distributions. The wettability map was obtained for all samples using local lattice-Boltzmann calculations on trapped ganglia and optimization on surface affinity parameters. The results were quantitatively compared with a previously developed geometrical contact angle determination method. The two synthetic cases were used to validate the results of the developed workflow, as well as to compare the wettability results with the geometrical analysis method. It is shown that the developed workflow accurately characterizes the wetting state in the synthetic porous media with an acceptable uncertainty and is better to capture extreme wetting conditions. For the three datasets of imaged fluid distributions, our results show that the obtained contact angle distributions are consistent with the geometrical method. However, the obtained contact angle distributions tend to have a narrower span and are considered more realistic compared to the geometrical method. Finally, our results show the potential of the proposed scheme to efficiently obtain wettability maps of porous media using X-ray images of multiphase fluid distributions. The developed workflow can help for more accurate characterization of the wettability map in the porous media using limited experimental data, and hence more accurate digital rock analysis of multiphase flow in porous media.

中文翻译：

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使用局部格子-玻尔兹曼模拟对多孔介质中的润湿进行空间表征

摘要

润湿性是影响多孔介质多相流的关键参数之一。润湿性由流体对岩石表面的亲和力决定，该亲和力因矿物非均质性、粗糙度、老化和孔隙空间几何形状等因素而变化。众所周知，天然岩石的润湿性在空间上存在变化，并且在孔隙尺度模拟研究中它仍然被普遍认为是一个常数参数。这种不充分的润湿性模型削弱了多孔介质中多相流的孔隙尺度模拟的准确性。原位可视化技术（例如 X 射线成像和显微断层扫描）的出现使我们能够更准确地表征润湿的空间分布。这种表征有多种方法。大多数包括在分段 X 射线图像中构建界面表面的网格表面，并且已知由于分辨率和表面平滑算法不足而产生显着误差。这项工作提出了一种使用局部晶格玻尔兹曼模拟空间确定润湿特性的新方法。该方案的计算效率很高，因为在进行晶格玻尔兹曼模拟之前，分段的 X 射线图像被划分为子域，从而实现快速模拟。为了测试所提出的方法，将其应用于具有已知润湿性的两个合成案例和三个成像流体分布数据集。使用捕获神经节的局部晶格玻尔兹曼计算和表面亲和力参数的优化获得了所有样品的润湿性图。结果与先前开发的几何接触角测定方法进行了定量比较。这两个合成案例用于验证所开发工作流程的结果，并将润湿性结果与几何分析方法进行比较。结果表明，所开发的工作流程以可接受的不确定性准确地表征了合成多孔介质中的润湿状态，并且能够更好地捕获极端润湿条件。对于成像流体分布的三个数据集，我们的结果表明获得的接触角分布与几何方法一致。然而，获得的接触角分布往往具有更窄的跨度，并且与几何方法相比被认为更真实。最后，我们的结果表明，所提出的方案具有利用多相流体​​分布的 X 射线图像有效获得多孔介质润湿性图的潜力。开发的工作流程可以帮助使用有限的实验数据更准确地表征多孔介质中的润湿性图，从而对多孔介质中的多相流进行更准确的数字岩石分析。