Using Chemical and Isotopic Data to Quantify Ionic Trapping of Injected Carbon Dioxide in Oil Field Brines

Abstract

Injection of carbon dioxide into depleted oil fields or deep saline aquifers represents one of the most promising means of long-term storage of this greenhouse gas. While the ultimate goal of CO2 injection in the subsurface is mineral storage of CO2 as carbonates, short-term (<50 year) storage of injected CO2 is most likely to be accomplished by ionic trapping of CO2 as bicarbonate ions (HCO3-) and hydrogeological trapping of molecular CO2. Here, we demonstrate a technique for quantifying ionic trapping of injected CO2 as HCO3- using geochemical data collected prior to and during 40 months of CO2 injection into a hydrocarbon reservoir at the International Energy Agency (IEA) Weyburn CO2 Monitoring and Storage Project, Saskatchewan, Canada. As a result of injection of CO2 with a low carbon isotope ratio (delta13C value), fluid and gas samples from four selected production wells showed an increase in HCO3- concentration and a decrease in delta13C values of HCO3- and CO2 over the observation period. Isotope and mass balance calculations indicate that, after 40 months of injection, approximately 80% of the HCO3- in the reservoir brines sampled from the four wells formed via dissolution and dissociation of injected CO2. This chemical and isotopic technique should be applicable to CO2 injection and storage in oil fields and in deep saline aquifers, provided there is sufficient carbon isotopic distinction between injected CO2 and baseline aquifer HCO3- and CO2.

Mineralization of carbon dioxide sequestered in volcanogenic sandstone reservoir rocks

“…The isotopic composition of the injected CO 2 may provide an ideal tracer for the assessment of the movement and the fate of injected CO 2 in the reservoir. If the CO 2 injected into mature oil-fields, saline aquifers or un-mineable coal seams has isotope ratios that are significantly different from those of naturally occurring carbon compounds in the reservoir, then δ 13 C values constitute a tracer for following the movement and reactions of injected CO 2 in the reservoir Emberley et al, 2005;Johnson et al, 2011;Myrttinen et al, 2010;Raistrick et al, 2006).…”

Hydrogeochemistry of surface and spring waters in the surroundings of the CO2 injection site at Hontomín–Huermeces (Burgos, Spain)

“…atmosphere, soil respiration, carbonate. Thus, the isotopic and chemical equilibrium of the C-bearing inorganic species can be used to trace CO 2 leakage if the injected CO 2 would have an isotopic carbon ratio that differs with respect to that already present (Raistrick et al, 2006). The ␦ 13 C-CO 2 values measured in the HH waters are clustering around −20‰ V-PDB and thus are more positive than those of the injected CO 2 at Ketzin.…”

The Relevance of Geochemical Tools to Monitor Deep Geological CO2 Storage Sites

“…the formation of carbonate minerals due to the reaction of the dissolved CO 2 with the host rocks, can be similarly performed. Raistrick et al (2006) and Myrttinen et al (2010) introduced and used the following carbon isotope balance calculation to determine the percentage of DIC from CO 2 dissolution in the water phase, and thus to quantify the geochemical trapping of injected CO 2 : 13 13 DICafterinj. DICbaseline 13 13 CO 2(g )inj.…”