Regional-scale brine migration along vertical pathways due to CO<sub>2</sub> injection – Part 1: The participatory modeling approach

Abstract

Abstract. Saltwater intrusion into potential drinking water aquifers due to the injection of CO 2 into deep saline aquifers is one of the potential hazards associated with the geological storage of CO 2 . Thus, in a site selection process, models for predicting the fate of the displaced brine are required, for example, for a risk assessment or the optimization of pressure management concepts. From the very beginning, this research on brine migration aimed at involving expert and stakeholder knowledge and assessment in simulating the impacts of injecting CO 2 into deep saline aquifers by means of a participatory modeling process. The involvement exercise made use of two approaches. First, guideline-based interviews were carried out, aiming at eliciting expert and stakeholder knowledge and assessments of geological structures and mechanisms affecting CO 2 -induced brine migration. Second, a stakeholder workshop including the World Café format yielded evaluations and judgments of the numerical modeling approach, scenario selection, and preliminary simulation results. The participatory modeling approach gained several results covering brine migration in general, the geological model sketch, scenario development, and the review of the preliminary simulation results. These results were included in revised versions of both the geological model and the numerical model, helping to improve the analysis of regional-scale brine migration along vertical pathways due to CO 2 injection.

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

“…The boundary conditions were already a major subject during the participatory modeling process. As a result, the boundary conditions of the model have been thoroughly revised after the expert workshop presented in Part 1 (Scheer et al, 2017). The boundary conditions at the top of the model domain were adjusted to allow for a more realistic baseflow in the shallow aquifers.…”

“…This fault zone is a permeable connection between the injection horizon and the shallow aquifers above the Rupelian clay barrier. The assumption of fluid migration via vertical pathways in sediments flanking salt structures is a matter of debate, which was also part of the discussion in the participatory modeling process (Part 1; Scheer et al, 2017). Based on LBEG (2012), "the contact zone between salt domes and the CO 2 sequestration horizon is assumed to be a zone of weakness, similar to geological faults".…”

“…During the participatory modeling process presented in Part 1 (Scheer et al, 2017), the results of simplified models were presented, where brine was injected instead of CO 2 . In this work, we consider further model simplifications and discuss their effects in detail.…”

“…From the very beginning, this research on brine migration was aimed at involving expert and stakeholder knowledge in the simulation of impacts during the injection of CO 2 into deep saline aquifers. Therefore, this work is split into two papers (Part 1 and Part 2), where Part 1 (Scheer et al, 2017) deals with the concept of "participatory modeling" as a means to involve external experts and stakeholders in the modeling process, and Part 2 deals with the technical findings relevant for modeling brine migration. The participatory modeling process in-A.…”