Abstract
Abstract. Saltwater intrusion into potential drinking water aquifers due to the injection of CO2 into deep saline aquifers is one of the hazards associated with the geological storage of CO2. Thus, in a site-specific risk assessment, models for predicting the fate of the displaced brine are required. Practical simulation of brine displacement involves decisions regarding the complexity of the model. The choice of an appropriate level of model complexity depends on multiple criteria: the target variable of interest, the relevant physical processes, the computational demand, the availability of data, and the data uncertainty. In this study, we set up a regional-scale geological model for a realistic (but not real) onshore site in the North German Basin with characteristic geological features for that region. A major aim of this work is to identify the relevant parameters controlling saltwater intrusion in a complex structural setting and to test the applicability of different model simplifications. The model that is used to identify relevant parameters fully couples flow in shallow freshwater aquifers and deep saline aquifers. This model also includes variable-density transport of salt and realistically incorporates surface boundary conditions with groundwater recharge. The complexity of this model is then reduced in several steps, by neglecting physical processes (two-phase flow near the injection well, variable-density flow) and by simplifying the complex geometry of the geological model. The results indicate that the initial salt distribution prior to the injection of CO2 is one of the key parameters controlling shallow aquifer salinization. However, determining the initial salt distribution involves large uncertainties in the regional-scale hydrogeological parameterization and requires complex and computationally demanding models (regional-scale variable-density salt transport). In order to evaluate strategies for minimizing leakage into shallow aquifers, other target variables can be considered, such as the volumetric leakage rate into shallow aquifers or the pressure buildup in the injection horizon. Our results show that simplified models, which neglect variable-density salt transport, can reach an acceptable agreement with more complex models.
Highlights
Any effort in investigating and developing the Carbon Dioxide Capture and Storage technology (CCS) unavoidably touches the social and political sphere and needs to take into account the broader societal debate
The results indicate that the initial salt distribution prior to the injection of CO2 is one of the key parameters controlling shallow aquifer salinization
Kissinger et al.: Part 2: A simulated case study in the North German Basin fluenced the setup of the geological model and the scenarios presented in this paper
Summary
Any effort in investigating and developing the Carbon Dioxide Capture and Storage technology (CCS) unavoidably touches the social and political sphere and needs to take into account the broader societal debate. (Tillner et al, 2013) consider brine-migration scenarios for a potential storage site in northern Germany using a multiphase (brine and supercritical CO2), multicomponent (H2O, NaCl, and CO2) model accounting for salt-dependent density differences They included several permeable and impermeable fault zones, thereby controlling leakage into overlying aquifers. (Walter et al, 2012, 2013) used a generic, horizontally stratified multilayer system with a circular fault zone surrounding the injection well at a certain distance They used a compositional multiphase model (water, supercritical CO2, NaCl) to calculate the brine flow into a shallow aquifer. This is followed by the analysis of the reduction of model complexity.
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