CO2 Injection in a Coal Seam – Insights from the European Carbolab Project with Focus on Water Geochemical Monitoring

Abstract

Abstract The CARBOLAB project is funded by the European program RFCS (Research Fund for Coal and Steel). It gathers six partners from Spain, France and Poland. One of the main tasks of this project is to perform in-situ CO 2 injection in a coal seam located at 464 m depth in the Montsacro pit, Asturias, Spain. Injection of CO 2 in coal seams is one of the options for climate change mitigation but it presents lots of uncertainties and technical difficulties. Therefore work is needed to better constraint the processes especially the adsorption of CO 2 and the subsequent desorption of CH4. This work consists in experimental laboratory work, modelling aspects and real tests. This paper is focused on this last topic and more specifically on the water monitoring aspects. Complementary investigations on the gas phase can be found in other works presented by Lafortune et al. in this conference. In-situ injection of CO 2 has been performed in July 2013 in one selected coal seam. The CO 2 is injected directly in the vein and monitoring boreholes are located at the wall and in the surrounding sedimentary formations. The aim is to get a detailed and representative overview of the consequences of the CO 2 injection. Here the focus is on the geochemical monitoring. Baseline acquisitions have been performed in 2012 and early 2013. This allowed to define a strategy mainly focused on the monitoring of the saturated zone albeit the site was initially thought to be drier. Acquisitions in the unsaturated zone (free gas phase) have also been done but in a less extent. Chemical logging of water saturated boreholes (GC1S and GC3N, parallel to the seam) revealed, even at short distance, the existence of different water masses from one side of the coal vein to the other. This is mainly linked to a difference in the amount of dissolved solids in water. During the injection experiment, no noticeable deviations from the baseline values were found for GC1S borehole. At the opposite, the bottom of GC3N experienced strong changes: decrease of more than 2.5 pH units, rise of the electrical conductivity (+29%) and of the alkalinity (+23%).