Aquifer storage and recovery (ASR) involves the injection of freshwater into an aquifer for temporary water storage and later use. Previous studies have shown that density-driven convection may render part of the injectant unrecoverable when ASR is implemented in a saline aquifer. Where heterogeneity creates a significant proportion of immobile groundwater, dual-domain (immobile and mobile porosities) effects also lead to reductions in the efficiency of ASR schemes. Presuming constant total porosity (sum of the mobile and immobile porosities), the combined effects of dual-domain properties and water density on ASR are investigated for the first time in the present study, using numerical modeling of otherwise similar conceptual models to previous ASR analyses. Results show that the interactions between the density effect and dual-domain mass transfer lead to complex controlling patterns of the density contrast, the ratio of immobile-mobile porosities, the parameterization of immobile-mobile solute exchange, and the number of cycles. The influence of these factors on mixing processes and the recovery efficiency (proportion of freshwater injectant recovered by extraction) during ASR are shown. Dual-domain effects, where they occur in aquifers, must be included explicitly in models to reproduce recovery efficiencies, especially during early cycles, unless the immobile porosity is very small or the conductance between mobile and immobile regions is at extremes. Otherwise, a single-domain model can be utilized. The findings of this research illustrate the influence of both density effects and dual-domain processes on ASR and the need to account for both in assessing ASR feasibility in complex hydrogeological settings.

中文翻译：

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密度和双域传质对含水层储存和回收的耦合效应

含水层储存和回收 (ASR) 涉及将淡水注入含水层，用于临时储水和以后使用。先前的研究表明，当在含盐含水层中实施 ASR 时，密度驱动的对流可能会导致部分注入剂无法回收。在异质性造成很大比例的固定地下水的情况下，双域（固定和移动孔隙度）效应也会导致 ASR 方案的效率降低。假设总孔隙度恒定（移动孔隙度和固定孔隙度之和），本研究首次研究了双域特性和水密度对 ASR 的综合影响，使用与先前 ASR 分析类似的概念模型的数值建模. 结果表明，密度效应和双域传质之间的相互作用导致了密度对比、固定-流动孔隙率比、固定-流动溶质交换参数化和循环次数的复杂控制模式。显示了这些因素对混合过程和 ASR 期间的回收效率（通过萃取回收的淡水注入剂的比例）的影响。含水层中出现的双域效应必须明确包含在模型中，以重现采收效率，尤其是在早期循环期间，除非固定孔隙度非常小或流动和固定区域之间的电导率处于极端水平。否则，可以使用单域模型。