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Zusammenfassung:
World-wide research projects addressing geological CO2 storage and geothermal heat provision highlighted two questions of uttermost importance for the feasibility of CO2 storage in saline aquifers which were not addressed by scientific research so far:
Endangerment of freshwater reservoirs by upward migration of brine from saline aquifers as a result of the pressure increase subsequent to a CO2 injection into a target storage formation.
Synergetic utilization of geothermal heat production and CO2 storage by implementation of pressure discharge wells.
Within the scope of the brine joint-project both questions were addressed in two main research topics. The first one comprised a feasibility study considering the detection of potential upward brine migration. Thereto, an integrated early warning system was developed involving a network of electrical resistivity tomography (ERT) as well as magnetotelluric (MT) and electromagnetic (EM) monitoring techniques. The objective was to detect upward brine migration as early as possible to employ appropriate. Different scenarios of brine migration effected by CO2 injection were simulated using coupled numerical models, whereas brine migration into freshwater-bearing reservoirs considered for drinking water supply was specifically taken into account. Furthermore, coupled hydro-geomechanical simulations allowed us to determine the role of existing faults by means of representing potential leakage pathways (Magri et al., 2013; Röhmann et al., 2013; Tillner et al., 2013a).
For validation of the integrated early warning concept, spatial and time-dependent distributions of the displaced brine determined during the computation of different migration scenarios were transformed into raw data and integrated into our ERT, MT and EM monitoring network model. These data were then applied for identification of network geometries required for successful monitoring of brine migration.
The second question was addressed by a theoretical study within the scope of the brine project taking into account if brine from pressure discharge wells, which are implemented to increase the overall CO2 storage capacity of the target formation, can be used in geothermal heat provision. Here, an enhanced management of the storage reservoir was investigated considering re-injection of the thermal water into deeper saline aquifers (Tillner et al., 2013b).
Our results demonstrate that a synergetic application of CO2 storage and geothermal heat production is generally feasible. Furthermore, a conceptual early warning system for detection of freshwater salinisation was developed, calibrated by laboratory and field tests (e.g. Wagner et al., 2013), and validated by numerical modelling studies.
