Werkendam long-term CO2 reactions by Marielle Koenen and Laura Wasch

An assessment of the long-term fate of CO2 in a reservoir is required for CO2 storage according to EU regulations. Assuming that CO2 will be successfully contained after injection, the long-term effects depend on the gas-water-rock interactions within the storage reservoir. These interactions can be investigated using experiments and geochemical modelling. The first are per definition short-term, while the latter use simplified representations of complex geological systems. Another way to investigate the long-term effects is provided by natural CO2 fields, the so called natural analogues. The natural CO2 field of Werkendam in the Netherlands is representative for numerous potential Dutch storage locations, both on- and offshore. These potential storage sites, including the P18-4 reservoir of the ROAD project, are mostly (future) depleted hydrocarbon reservoirs, located in Triassic sandstone formations in the Dutch subsurface. The Werkendam gas field contains over 70% of CO2. The CO2 has probably been present in the reservoir for millions of year. Investigations into this ‘natural lab’ provided insights on the gas-water-rock interactions on geological time scales, insights which were used to calibrate a geochemical model on the long-term fate of CO2.