Small-Scale ASR Between Flow Barriers in a Saline Aquifer

Standard aquifer storage and recovery (ASR) methods struggle in brackish or saline aquifers due to buoyancy effects that cause fresh water to rise and become unrecoverable. While large-scale ASR systems have been studied, small-scale applications remain underexplored. Previous research has shown that flow barriers can help contain fresh water in such aquifers, but the effectiveness of these barriers is not fully understood. The role of density differences in water movement is a known factor, but how it interacts with barrier placement remains unclear. Hydraulic conductivity and pumping rates are also known to influence recovery efficiency, but their combined effects in saline aquifers are not well characterized. Numerical modeling has been used to simulate aquifer behavior, but field and lab experiments are needed to validate these models. This gap motivated the current study to explore how flow barriers affect small-scale ASR in saline aquifers. By combining flow tank experiments with numerical simulations, the study aims to clarify the mechanisms behind recovery efficiency in these challenging environments.

This study investigates how flow barriers can improve small-scale ASR in saline aquifers by preventing lateral expansion of fresh water. The goal is to determine the effectiveness of different injection and recovery methods—constant flux versus constant head—in such settings. The researchers aim to understand how factors like density differences, hydraulic conductivity, and barrier placement influence recovery rates. By using both laboratory experiments and numerical modeling, the study seeks to provide a comprehensive view of the physical processes involved. The motivation stems from the need to optimize ASR for brackish and saline aquifers where buoyancy effects hinder recovery. The study also explores the impact of cyclic operation on recovery efficiency. Understanding these factors is essential for designing practical ASR systems in challenging hydrological conditions. The findings could help guide the placement and design of flow barriers to maximize recovery rates in saline aquifers.

The study uses a combination of flow tank experiments and numerical modeling to simulate ASR in saline aquifers. A flow tank setup allows for controlled injection and recovery of fresh water in a brackish or saline environment. Flow barriers are partially inserted into the tank to mimic real-world conditions. The experiments track groundwater flow and mixing during injection, storage, and recovery phases. Two operational methods are tested: constant flux and constant head. Numerical modeling complements the experiments by simulating the same conditions with varying parameters. The models incorporate density differences, hydraulic conductivity, and barrier configurations. The study evaluates recovery efficiency under different pumping rates and barrier placements. The spatial distribution of flow velocity is also analyzed to determine its impact on leakage and upconing effects.

The experiments showed that recovery rates of fresh water in saline aquifers can reach up to 90% in later cycles when using constant flux injection. In the first cycle, recovery rates were around 65%, indicating a learning effect or adaptation in the system. Constant head injection resulted in lower recovery efficiency compared to constant flux. The spatial variation in flow velocity across the storage zone was found to influence recovery efficiency. During injection, fresh water tends to leak underneath the flow barriers due to velocity gradients. During recovery, salt water upconing occurs, reducing the purity of recovered water. The presence of flow barriers significantly improved recovery rates by limiting lateral expansion of fresh water. The study found that cyclic operation enhances recovery efficiency over time. The numerical models confirmed the experimental results, validating the observed trends in flow behavior and mixing.

The study concludes that flow barriers can significantly improve recovery efficiency in small-scale ASR operations in saline aquifers. The use of constant flux injection methods yields higher recovery rates compared to constant head methods. Recovery efficiency increases with each cycle, suggesting that the system adapts over time. The spatial variation in flow velocity is a key factor influencing leakage and upconing effects. The presence of flow barriers is essential in preventing lateral expansion of fresh water, which enhances recovery rates. The study also found that density differences and hydraulic conductivity play a role in determining the effectiveness of ASR in saline aquifers. The numerical models align with the experimental results, confirming the observed trends in flow behavior. These findings suggest that optimizing barrier placement and injection methods can improve ASR performance in saline aquifers.