FRESHWATER SALINIZATION – ANALYSIS AND MODELLING WITH REGARD TO CO2 STORAGE IN SALINE AQUIFERS

Upward brine migration is considered as a particularly important endangerment for freshwater resources as a result of CO₂ storage in deep saline aquifers. Thereby, the understanding of the geological underground and the natural and induced migration processes are of great importance at potential storage sites. Within the framework of the project ”brine – CO₂ storage in Eastern Brandenburg”, funded by the BMBF (Project 03G0758), hydrogeological und geophysical investigations and modelling of the fresh and saltwater dynamics are carried out around a prospective storage site in the Northeastern German Basin. The site is located at a salt anticline structure with a storage reservoir in sandstone formations at a depth of about 1.000 m.

Regional geological models were implemented with an extent from 40 x 40 km² up to 70 x 80 km² representing the reservoir, the overburden rocks and the unconsolidated rocks of the Cenozoic. The unconsolidated rocks of the Cenozoic are the regional freshwater aquifers and reach more than 250 m depth. The major boundary between the freshwater and saltwater is an Oligocen clay formation (Rupelian clay). Buried Quaternary channels have complicated the internal structure of cenozoical deposits and led locally to erosion of the Rupelian clay resulting in possible migration paths.

Hydrochemical investigations by means of analysis of geochemical indicators as well as stable isotopes show the migration of brines from the Mesozoic overburden rocks into parts of the freshwater aquifers and the existence of salinization zones in the investigation area. These are connected to fault zones in the Mesozoic rocks and the quarternary erosion channels.

First numerical simulation studies of the reservoir and the overburden rocks aimed at the sensitivities of pressure elevation in the target storage formations with regard to the conductivity of the surrounding fault systems, as well as reservoir properties. Spatial and time-dependent distributions of the displaced brine and reservoir pressure development were determined during several migration scenarios. Further efforts will connect the simulations in the reservoir, the overburden and the freshwater aquifers to develop a better understanding of the potential salinization processes at the actual state and under the conditions of CO₂ storage.