Mineral and geochemical attributes of the midcontinent rift sequence; An application for deep carbon dioxide sequestration

The potential for using the Oronto Group of the Midcontinent Rift (MCR) Sequence for CO2 sequestration has been disparaged because of low porosity-permeability characteristics, which are largely a result of extensive calcite cementation. This study investigated the potential for using the MCR as a target for CO2 sequestration by examining reactions involving detrital host-rock minerals at high pressure-temperature conditions that could provide dissolved Ca2+, Mg2+, and Fe2+, and then precipitating these cations as carbonate minerals. The effect of carbonic acid on cement dissolution was also evaluated with respect to enhancing porosity and permeability. The Oronto Group sediments were enriched in CaO and MgO (5-12 wt%), and dominated by volcanic-lithic fragments with traces of alkali-feldspar, plagioclase, muscovite, quartz, chlorite, illite and smectite. The overlying Bayfield Group sediments are feldspathic quartz arenites with up to 17% porosity, however, they have low abundances of CaO and MgO (2-saturated deionized water at 90⁰C in Teflon vessels, or mildly acidic nitric acid solution in room-temperature core-flooding experiments to evaluate reactions under potential sequestration conditions. Rapid dissolution of calcite cement was noted in short-term tests (1.6 - 20 mg Ca/cm2.day), while supersaturated conditions were achieved with the associated precipitation of carbonate minerals in longer-term (101.9 day) experiments following the neutralization of carbonic acid and associated pH rise. The potential of using the Oronto Group as a CO2 sequestration target is favored by its carbonate mineralization potential, but hindered by its limited permeability, even for samples that displayed porosity enhancement following calcite cement dissolution. --Abstract, page iii