Exploring the Impacts of Source Condition Uncertainties on Far‐Field Brine Leakage Plume Predictions in Geologic Storage of CO₂: Integrating Intermediate‐Scale Laboratory Testing With Numerical Modeling

Abstract

Natural fissures/faults or pressure‐induced fractures in the caprock confining injected CO2 have been identified as a potential leakage pathways of far‐field native brine contaminating underground sources of drinking water. Developing models to simulate brine propagation through the overlaying formations and aquifers is essential to conduct reliable pre‐ and post‐risk assessments for site selection and operation, respectively. One of the primary challenges of performing such simulations is lack of adequate information about source conditions, such as hydro‐structural properties of caprock fracture/fault zone and the permeability field of the storage formation. This research investigates the impact of source condition uncertainties on the accuracy of leaking brine plume predictions. Prediction models should be able to simulate brine leakage and transport in complex multilayered geologic systems with interacting regional natural and leakage flows. As field datasets are not readily available for model testing and validation, three comprehensive intermediate‐scale laboratory experiments were used to generate high‐resolution spatiotemporal data on brine plume development under different leakage scenarios. Experimental data were used to validate a flow and transport model developed using existing code FEFLOW to simulate brine plume under varying source conditions. Spatial moment analysis was conducted to evaluate how uncertainty in source conditions impacts brine migration predictions. Results showed that inaccurately prescribing the permeability field of storage formation and caprock fractures in models can cause errors in leakage pathway and spread predictions up to ∼19% and ∼100%, respectively. These findings will help in selecting and characterizing storage sites by factoring in potential risks to shallow groundwater resources.

Monitoring Brine Leakage From Deep Geologic Formations Storing Carbon Dioxide: Design Framework Validation Using Intermediate‐Scale Experiment

“…Concentration data was generated through chemically analyzing the collected aqueous samples from the selected septa-ports by the OD framework using an ion chromatography (IC) system (Dionex Aquion combined with autosampler Dionex As-Dv). More details of the sampling approach used in this study can be found in Askar et al (2021). The hydraulic heads were measured using the manometers selected by the OD framework as well, twice a day.…”

“…FEFLOW solves the groundwater flow and transport equations using a continuous finite-element scheme (Diersch, 2014). It is worth mentioning that a FEFLOW-based model was validated by Askar et al (2021) using experimental data for its ability to capture the migration of a bromide plume under multi-dimensional complex flow fields in a system with three geologic zones similar to this study. The solution domain of the base-models was discretized with a high-resolution mesh (∼190,000 triangular elements) to represent the heterogenous sand packing of Zone 3 and the sand layers of Zone 2.…”

“…Design of such experiments requires: (a) downscaling the actual depths of the geological formations relevant to this problem, (b) simulating the vertical brine plume within the laboratory space limitations, and (c) mimicking the dominant and complex physical processes that occur in the field. Askar et al (2021) developed a novel approach to simulate the vertical brine migration from a CO 2 storage zone to a shallow aquifer across multiple overlying formations using a horizontal soil tank (Figures 2a vs. 2b) due to space limitations in the laboratory.…”

“…One of the constraints of using this approach is the necessity of minimizing the density effects on the plume development (Askar et al, 2021). Therefore, the concentration of the injected brine surrogate (NaBr tracer) was set at a considerably low value during the experiment to eliminate plume sinking in the vertical direction of the tank.…”

“…More details of the tank construction, heterogeneity design, and packing procedures can be found in Askar et al. (2021).…”