The formation of viscous limited saturation zones behind rapid drainage fronts in porous media
The formation of viscous limited saturation zones behind rapid drainage fronts in porous media
复制标题
DOI：
10.1002/2015wr016980
复制
发表时间：
2015-12
影响因子：
5.4
通讯作者：
F. Hoogland;P. Lehmann;D. Or
中科院分区：
文献类型：
--
作者：
F. Hoogland;P. Lehmann;D. Or
多孔介质的排水特性是由重力、毛细管力和粘性力之间的相互作用形成的，从而导致复杂的相侵入模式和动力学。我们提出了一个机制模型的粘性分离的临时相滞留在快速移动的排水战线。在前尖端（最深穿透空气指的尖端）后面形成的粘性受限区域以较慢的速率排出，其特征时间尺度τ由介质的水力特性表示的水力解耦决定。饱和度变为粘性滞留（暂时截留）的区域由临界含水量θcrit确定，该临界含水量θcrit定义了前端后面的粘性长度LV。预测临界含水量θcrit和特征二次时标τ的理论与使用中子射线照相术和直接成像测量的排水特性非常一致。理论预测的临界含水量θcrit随着排水速率的增加而增加。观察到的缓慢排水时间尺度τ作为平均排水速率的函数，取决于临界含水量θcrit以及由此产生的滞留液体体积增加和粘性有限区域的电导率增加的抵消效应。排水分区的概念说明了如何增加流速提高粘性限制的程度背后的主要排水战线。新的见解可能有助于不混溶流体驱替的管理，量化实验测量中的平均效应（对pc-S关系的动态影响），并解释场容量现象的一些基础。
Drainage characteristics of porous media are shaped by an interplay between gravitational, capillary and viscous forces that result in complex phase invasion patterns and dynamics. We propose a mechanistic model for viscous separation of temporary phase detention behind rapidly moving drainage fronts. The viscous‐limited region forming behind the front tip (tip of furthest penetrated air finger) drains at a slower rate with a characteristic time scale τ dictated by hydraulic decoupling expressed by the hydraulic properties of the medium. The region where saturation becomes viscously detained (temporarily entrapped) is determined by a critical water content θcrit that defines a viscous length LV behind the front tip. Theory developed to predict the critical water content θcrit and the characteristic secondary timescale τ was in good agreement with measured drainage characteristics using neutron radiography and direct imaging. The observed critical water content θcrit increased with higher drainage rates as predicted by theory with consideration of a percolation threshold. The observed slow drainage timescale τ as a function of mean drainage rate depended on the critical water content θcrit and the resulting counteracting effects of increased detained liquid volume and increased conductivity of the viscous limited region. The concept of drainage zonation illustrates how increasing flow rates enhances the extent of viscous limitations behind the main drainage front. The new insights could be useful for management of immiscible fluid displacement, quantification of averaging effects in experimental measurements (dynamic effects on pc‐S relationship), and explain some of the underpinnings of the field capacity phenomenon.