Author : Virginia M. Marcon
Publisher :
ISBN 13 : 9781303736643
Total Pages : 159 pages
Book Rating : 4.7/5 (366 download)
Book Synopsis Carbon Dioxide-water-rock Interaction in a Carbonate Reservoir Capped by a Clay by : Virginia M. Marcon
Download or read book Carbon Dioxide-water-rock Interaction in a Carbonate Reservoir Capped by a Clay written by Virginia M. Marcon and published by . This book was released on 2013 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: Deep geologic formations are attractive reservoirs for geologic carbon sequestration (GCS) due to their ability to store hydrocarbons for millions of years. The technology needed for injecting CO2 into these geologic formations was established through the oil and gas industry for enhanced oil recovery (EOR) and enhanced gas recovery (EGR). However, there are some risks associated with CO2 injection such as leakage of inorganic compounds into overlying potable aquifers. Since it is difficult to avoid leakage in these systems, understanding how leaks may affect the chemistry of overlying potable aquifers is crucial. Two groups of hydrothermal experiments were performed to evaluate metal mobilization and mechanisms of release from within a storage reservoir. The first group of experiments react idealized Desert Creek limestone and/or Gothic Shale, formations in the Paradox Basin, Utah, at 160C and 25MPa in a brine (I = 3.3m). These experiments investigated the release of harmful metals from two zones within a sequestration injection reservoir: at the caprock-reservoir boundary and deeper within the reservoir. Experimental results show that CO2 injection decreases the pH by 1 to 2 units; concomitant mineral dissolution produces elevated Ba, Cu, Fe Pb and Zn concentrations in the brine. Concentrations subsequently decrease to approximately steady state values after 120-330 hours as a result of secondary mineralization of Ca-Mg-Fe carbonates, metal sulfides (i.e. Fe, As, Ag and Co sulfides), sulfates and clays. Iron, an element of secondary concern, and lead exceed the EPA regulated limits in both experiments at termination; Ba, Cu and Zn concentrations remain below the U.S. Environmental Protection Agency (EPA) maximum contaminate limits (MCL). Transition elements Cd, Cr, Cu and Zn as well as Pb, behave in a similar manner, increasing in concentration with injection but continually decreasing after about 830 hours until termination of the experiment. Nickel, not a regulated element, is also readily mobilized, and is associated with human health concerns at elevated concentrations. If brines leak from a storage reservoir and mix with a potable aquifer, the experimental results suggest that Ba, Cu and Zn will not be contaminants of concern, but Fe, Ni and Pb may require careful attention. However, experimentally observed trends of decreasing trace metal concentrations suggest that these metals could become less of a concern during the life of a carbon repository. Finally, the caprock plays an active role in trace metal evolution in the system. The caprock provides a large source of metals, but secondary mineralization and adsorption may remove metals of concern from solution. The second group of hydrothermal experiments reacted an idealized carbonate injection reservoir (Fe-rich dolomite) and caprock (illite) in a water (I =0.1m) to investigate the potential for metal mobilization and precipitation within a GCS scenario. Experiments investigated three locations within a sequestration reservoir: deep within the storage reservoir, within the caprock and at the caprock-reservoir boundary. The experiments were reacted for ~55 days: 17 days to approach steady state before CO2 is injected and 38 days to monitor changes from CO2 injection. Several major and minor ions, total dissolved CO2 and pH were monitored throughout the duration of the experiments. In all three experiments, Ca, Fe, Mg, Mn, SiO2 and SO4 increased as a result of CO2-injection, but subsequently decline through the termination of the experiments. The aqueous data supported by geochemical equilibrium modeling, FESEM images and XRD results indicate initial dissolution of illite and dolomite minerals followed by re-precipitation of Ca, Mg, Fe-carbonates, Fe, Ag-sulfides, Ba-sulfates, clays and Co, Cr, Cu, Fe, Zn-metal-oxides. Trace metals in these experiments did not exceed the U.S. EPA's primary or secondary MCL, but geochemical patterns denote valuable information for metal release, co-precipitation and adsorption of metals in a sequestration scenario. Experiments replicating an idealized carbonate injection reservoir show that metals are more readily mobilized than in experiments containing a caprock. Once the caprock is included in the system, water chemistry, FESEM and modeling results suggest increased adsorption and co-precipitation of the potentially harmful metals, which removes mobilized metals from solution. Barium, Sr and Fe are potential elements of concern in a sequestration scenario due to mobility of the metals.
