Saturation Dependence of Non-Fickian Transport in Porous Media
Saturation Dependence of Non-Fickian Transport in Porous Media
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DOI：
10.1029/2018wr023554
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发表时间：
2019-02-01
影响因子：
5.4
通讯作者：
Sahimi, Muhammad
中科院分区：
文献类型：
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作者：
Hasan, Sharul;Joekar-Niasar, Vahid;Sahimi, Muhammad
在多孔介质中的两相流中，蒸发通道可以在流体动力学上分为流动区和停滞区。高度可变的速度场填充的载体流体的孔隙空间中导致显着的差异，在运输时间尺度的两个区域，不能解释的菲克（高斯）对流-弥散方程。相对于达西尺度的研究，到目前为止，相对有限的孔隙尺度的研究一直致力于两相流中的传输特性的表征。在本文中，我们报告的结果，在稳态两相流通过多孔介质中使用的孔隙网络模型，作为一个放大工具的对流-弥散输运的计算机模拟。模拟结果放大直接估计达西尺度传输系数和属性，即停滞饱和度，流动和停滞区域之间的传质系数，和流动区域的纵向分散。流动-不流动模型是模拟多孔介质中非Fickian输运的最常用模型之一，用于通过对流出物浓度剖面的逆模拟来估计输运性质。直接估计的参数之间的不一致，通过移动-不移动的基础上的逆建模得到的那些意味着后者描述在两相流中的传输的根本缺点。模拟结果表明，相对渗透率可以用来获得停滞饱和度的准确估计，它将两相达西定律和输运联系起来。Plain Language小结通过多孔介质的两相流中的溶质输运是许多工业和自然过程的重要课题，例如农业中部分饱和土壤中的营养物输运，油藏中化学品的输运以提高石油采收率，或土壤修复。在不同的应用中，多相流动和传输的建模是必不可少的，以改善设计和操作条件。因此，需要改进这些模型的预测能力。为了评估嵌入在一个最常用的理论，被称为移动-不动理论的假设，我们已经进行了这些物理过程的孔隙尺度模拟。通过放大模拟结果，我们直接估计的输运性质，并将它们与使用移动-不移动理论的逆模拟结果进行比较。直接和间接估计的结果之间存在显着差异，这意味着在移动-不移动理论的潜在缺陷。此外，它已被讨论，潜在的两相相对渗透率数据可以用作代理估计停滞（不动）饱和度，将两相达西理论与运输模型。
In two-phase flow through porous media, the percolating pathways can be hydrodynamically split into the flowing and stagnant regions. The highly variable velocity field in the pore space filled by the carrier fluid leads to significant differences in the transport time scales in the two regions that cannot be explained by the Fickian (Gaussian) advection-dispersion equation. In contrast with the Darcy-scale studies, up to now, relatively limited pore-scale studies have been devoted to the characterization of transport properties in two-phase flow. In this paper, we report on the results of computer simulation of advection-dispersion transport in steady state two-phase flow through porous media using a pore network model, employed as an upscaling tool. The simulation results are upscaled to directly estimate the Darcy-scale transport coefficients and properties, namely, stagnant saturation, the mass transfer coefficient between the flowing and stagnant regions, and the longitudinal dispersion in the flowing regions. The mobile-immobile model, one of the most commonly used models for simulating non-Fickian transport in porous media, is used to estimate the transport properties using the inverse modeling of effluent concentration profiles. The disagreement between the directly estimated parameters and those obtained by the mobile-immobile-based inverse modeling implies fundamental shortcomings of the latter for describing transport in two-phase flow. The simulation results indicate that the relative permeabilities may be used to obtain accurate estimates of the stagnant saturation, which link two-phase Darcy's law and transport.Plain Language Summary Solute transport in two-phase flow through porous media is an important topic for many industrial and natural processes such as nutrient transport in partially saturated soils in agriculture, transport of chemicals in oil reservoirs for enhanced oil recovery, or in soil remediation. Modeling multiphase flow and transport in different applications is essential to improve the design and operational condition. Hence, the predictive capabilities of such models need to be improved. To evaluate the assumptions embedded in one of the most commonly used theories, referred to as the mobile-immobile theory, we have performed pore-scale simulations of these physical processes. By upscaling the simulation results, we directly estimated the transport properties and compared them with the inverse modeling results using the mobile-immobile theory. There is a significant discrepancy between the directly and indirectly estimated results that imply the potential shortcomings in the mobile-immobile theory. Moreover, it has been discussed that potentially the two-phase relative permeability data can be used as a proxy to estimate the stagnant (immobile) saturation that will link two-phase Darcy theory with the transport models.