Niko Kampman

Fluid-Mineral Reactions and Trace Metal Mobilization in an Exhumed Natural CO2 Reservoir, Green River, Utah

Red sandstones near Green River, Utah (United States), have been bleached by diagenetic fluids. Field relationships, modeling, fluid inclusion and isotopic data suggest that the causal fluid was a CO2-charged brine, distinguishing this site from hydrocarbon-related bleaching elsewhere on the Colorado Plateau. Mineralogical and chemical profiles from unbleached to bleached sandstone show that bleaching is related to hematite dissolution and precipitation of a 1–2 cm band of secondary oxide and carbonate at the reaction front. Trace metals are mobilized by the fluid and concentrated near the reaction front. High-flux fluid pathways are more heavily altered with large-scale secondary calcite and iron oxide precipitation. Changes may be modeled by a reaction with stoichiometry 20Fe2O3 + 5CH4 + 64CO2 + 19H2O + 11H+ = 30Fe2+ + 10FeHCO3+ + 59HCO3–. The Fe-rich, reduced fluid precipitates iron-oxides and carbonate at the reaction front between bleached and unbleached sandstone. These findings make the site an analogue for processes occurring over long time scales in geological carbon storage projects. Trace metals moblized by CO2-charged brines are likely to be rapidly re-precipitated at reaction fronts.

Observational evidence confirms modelling of the long-term integrity of CO2-reservoir caprocks

Storage of anthropogenic CO2 in geological formations relies on a caprock as the primary seal preventing buoyant super-critical CO2 escaping. Although natural CO2 reservoirs demonstrate that CO2 may be stored safely for millions of years, uncertainty remains in predicting how caprocks will react with CO2-bearing brines. This uncertainty poses a significant challenge to the risk assessment of geological carbon storage. Here we describe mineral reaction fronts in a CO2 reservoir-caprock system exposed to CO2 over a timescale comparable with that needed for geological carbon storage. The propagation of the reaction front is retarded by redox-sensitive mineral dissolution reactions and carbonate precipitation, which reduces its penetration into the caprock to ∼7 cm in ∼105 years. This distance is an order-of-magnitude smaller than previous predictions. The results attest to the significance of transport-limited reactions to the long-term integrity of sealing behaviour in caprocks exposed to CO2.

On the use and abuse of N2 physisorption for the characterization of the pore structure of shales

PIETER BERTIER , KEVIN SCHWEINAR, HELGE STANJEK, AMIN GHANIZADEH, CHRISTOPHER R. CLARKSON, ANDREAS BUSCH, NIKO KAMPMAN, DIRK PRINZ, ALEXANDRA AMANN-HILDENBRAND, BERNHARD M. KROOSS, and VITALIY PIPICH Clay & Interface Mineralogy, RWTH-Aachen University, Bunsenstr. 8, D-52072 Aachen, Germany Department of Geoscience, University of Calgary, Calgary, Canada Shell Global Solutions International, Kessler Park 1, 2288 GS Rijswijk, The Netherlands Dynchem, Saarstrasse 98, D-52062 Aachen, Germany Institute for Petroleum & Coal, RWTH-Aachen University, Lochnerstr. 2, D-52062 Aachen, Germany Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstrasse 1 85747 Garching, Germany e-mail: Pieter.Bertier@emr.rwth-aachen.de