Articles | Volume 21, issue 6
Hydrol. Earth Syst. Sci., 21, 2751–2775, 2017
Hydrol. Earth Syst. Sci., 21, 2751–2775, 2017

Research article 09 Jun 2017

Research article | 09 Jun 2017

Regional-scale brine migration along vertical pathways due to CO2 injection – Part 2: A simulated case study in the North German Basin

Alexander Kissinger1, Vera Noack2, Stefan Knopf2, Wilfried Konrad3, Dirk Scheer4, and Holger Class1 Alexander Kissinger et al.
  • 1Department of Hydromechanics and Modelling of Hydrosystems, University Stuttgart, Pfaffenwaldring 61, 70569 Stuttgart, Germany
  • 2Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hanover, Germany
  • 3DIALOGIK, Lerchenstraße 22, 70176 Stuttgart, Germany
  • 4ITAS, Karlsruhe Institute of Technology, Karlstrasse 11, 76133 Karlsruhe, Germany

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.

Short summary
Stakeholder participation in numerical modeling of brine migration due to injection of CO2 into deep saline aquifers is tested in this work. Part 1 reports the process of participatory modeling on the development of a numerical model and Part 2 discusses essential technical findings obtained through this model showing that notable increases in salt concentrations are confined to regions where they were already high a priori and where barrier layers are discontinuous.