Pore-Scale Simulation of Dispersion in Porous Media
Pore-Scale Simulation of Dispersion in Porous Media
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DOI：
10.2118/110228-pa
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发表时间：
2009-12-01
期刊：
影响因子：
3.6
通讯作者：
Lake, L. W.
中科院分区：
文献类型：
--
作者：
Garmeh, G.;Johns, R. T.;Lake, L. W.
油气藏中混相气与油的混合降低了气的有效强度，这会对可混性和采收率产生不利影响。然而，在使用非常大的网格块的油藏模拟中，油藏中发生的真实混合的水平被广泛争论并且经常被忽略。大的网格块创建人为的大的混合，可能会导致错误的预测石油recovery.This本文检查混合发生在多孔介质中的单相流在一个连接的网络孔隙求解。我们区分真正的混合，可以减少有效强度的可混溶气体或表面活性剂从对流扩散引起的明显的混合。这项工作不同于网络模型，因为我们直接求解Navier-Stokes方程和对流扩散方程，以确定孔隙内任何位置的速度和浓度。利用多个不同排列的颗粒模拟了串联和层状非均质多孔介质中的流动。我们考虑段塞、连续和部分注入以及回波测试（单井示踪剂测试）和传输测试（井间示踪剂测试）。我们匹配的浓度从孔隙尺度模拟的分析对流色散解决方案，包括横向和纵向色散coefficients. Results的结果表明，对于流在串联和层，回声和传输纵向色散变得相等，并达到一个渐近值，如果完全混合的横截面垂直于流发生。在实践中，分散性的渐近值可能永远不会达到，这取决于井网规模的非均质性和井距。横向色散系数也是尺度相关的，但它们随着行进距离而减小。我们进一步证明了经典的Perkins-Johnston关系之间的扩散系数和流体速度。我们的结论是，回波色散率是真实的多孔介质中的混合的可靠指标。
Mixing of miscible gas with oil in a reservoir decreases the effective strength of the gas, which can adversely affect miscibility and recovery efficiency. The level of true mixing that occurs in a reservoir, however, is widely debated and often ignored in reservoir simulation in which very large grid blocks are used. Large grid blocks create artificially large mixing that can cause errors in predicted oil recovery.This paper examines mixing that occurs in porous media by solving for single-phase flow in a connected network of pores. We differentiate between true mixing that can reduce the effective strength of a miscible gas or surfactant from apparent mixing caused by convective spreading. This work differs from network models in that we directly solve the Navier-Stokes equation and the convection-diffusion equation to determine the velocities and concentrations at any location within the pores. Flow in series and layered heterogeneous porous media are modeled through use Of many grains in different arrangements. We consider slug, continuous, and partial injection as well as echo tests (single-well tracer tests) and transmission tests (interwell tracer tests). We match the concentrations from the pore-scale simulations to the analytical convection-dispersion solution that includes both transverse- and longitudinal-dispersion coefficients.The results show that for flow in series and in layers, echo- and transmission-longitudinal dispersivities become equal and reach an asymptotic value if complete mixing over a cross section perpendicular to flow has occurred. In practice, the asymptotic value of dispersivity may never be reached, depending on pattern-scale heterogeneity and well spacing. Trans verse-dispersion coefficients also are scale dependent, but they decrease with traveled distance. We further demonstrate that the classical Perkins-Johnston relationship between longitudinal-dispersion coefficient and fluid velocity is obtained. We conclude that echo dispersivities are reliable indicators of true mixing in porous media.