Torkzaban Saeed, Bradford Scott A, Vanderzalm Joanne L, Patterson Bradley M, Harris Brett, Prommer Henning
CSIRO Land and Water, Glen Osmond, SA 5064, Australia.
US Salinity Laboratory, USDA, ARS, Riverside, CA, United States.
J Contam Hydrol. 2015 Oct;181:161-71. doi: 10.1016/j.jconhyd.2015.06.005. Epub 2015 Jun 19.
The release and retention of in-situ colloids in aquifers play an important role in the sustainable operation of managed aquifer recharge (MAR) schemes. The processes of colloid release, retention, and associated permeability changes in consolidated aquifer sediments were studied by displacing native groundwater with reverse osmosis-treated (RO) water at various flow velocities. Significant amounts of colloid release occurred when: (i) the native groundwater was displaced by RO-water with a low ionic strength (IS), and (ii) the flow velocity was increased in a stepwise manner. The amount of colloid release and associated permeability reduction upon RO-water injection depended on the initial clay content of the core. The concentration of released colloids was relatively low and the permeability reduction was negligible for the core sample with a low clay content of about 1.3%. In contrast, core samples with about 6 and 7.5% clay content exhibited: (i) close to two orders of magnitude increase in effluent colloid concentration and (ii) more than 65% permeability reduction. Incremental improvement in the core permeability was achieved when the flow velocity increased, whereas a short flow interruption provided a considerable increase in the core permeability. This dependence of colloid release and permeability changes on flow velocity and colloid concentration was consistent with colloid retention and release at pore constrictions due to the mechanism of hydrodynamic bridging. A mathematical model was formulated to describe the processes of colloid release, transport, retention at pore constrictions, and subsequent permeability changes. Our experimental and modeling results indicated that only a small fraction of the in-situ colloids was released for any given change in the IS or flow velocity. Comparison of the fitted and experimentally measured effluent colloid concentrations and associated changes in the core permeability showed good agreement, indicating that the essential physics were accurately captured by the model.
含水层中原位胶体的释放和滞留对有管理的含水层补给（MAR）方案的可持续运行起着重要作用。通过在不同流速下用反渗透处理（RO）水置换原生地下水，研究了固结含水层沉积物中胶体的释放、滞留以及相关的渗透率变化过程。当出现以下情况时，会发生大量胶体释放：（i）原生地下水被低离子强度（IS）的RO水置换，以及（ii）流速逐步增加。注入RO水时胶体的释放量和相关的渗透率降低取决于岩心的初始粘土含量。对于粘土含量约为1.3%的低粘土含量岩心样品，释放的胶体浓度相对较低，渗透率降低可忽略不计。相比之下，粘土含量约为6%和7.5%的岩心样品表现出：（i）流出液胶体浓度增加近两个数量级，以及（ii）渗透率降低超过65%。当流速增加时，岩心渗透率得到逐步改善，而短暂的水流中断则使岩心渗透率大幅增加。胶体释放和渗透率变化对流速和胶体浓度的这种依赖性与由于流体动力桥接机制在孔隙收缩处的胶体滞留和释放一致。建立了一个数学模型来描述胶体的释放、传输、在孔隙收缩处的滞留以及随后的渗透率变化过程。我们的实验和模拟结果表明，对于IS或流速的任何给定变化，只有一小部分原位胶体被释放。拟合的和实验测量的流出液胶体浓度以及岩心渗透率的相关变化之间的比较显示出良好的一致性，表明该模型准确地捕捉到了基本物理过程。
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