IDENTIFYING THE MINERALOGICAL CHANGES IN SHALE CAPROCKS FROM DEEP CO2 GEOSEQUESTRATION BY USING XRD AND RAMAN SPECTROSCOPY

Deep saline aquifers have been explored for CO₂ sequestration in order to reduce the emission of greenhouse gases. This sequestration practice involves the injection of a CO₂ steam into high porosity and permeability reservoir, contained by one or more overlying low permeability formations that function as a seal. In field conditions CO₂ is less dense than the formation fluids, thus it rises to the base of the seal and reacts with the caprocks. In order to understand the feasibility of a sequestration in deep saline aquifers the impermeable caprock formation and its interactions with CO₂ should be investigated. It is known that CO₂ could decrease the pH of the formation fluids , potentially driving fluid-rock interaction and CO₂ leakage. In this study, X-ray Diffraction (XRD) and Raman Spectroscopy are used to assess the mineralogical changes in shale formation. Raman Spectroscopy is particularly useful in terms of identifying both organic and inorganic phases. XRD is employed to determine the changes in mineralogical contents after the interaction with CO₂. The Conasauga Shale from the Black Warrior Basin, which contains Quartz, Calcite, Dolomite, Albite, Illite, Chlorite and Pyrite minerals, was used in the experiments. Powdered shale samples were reacted with pure gaseous CO₂, pure gaseous CH₄ are used to assess chemical interactions. In order to mimic the field condition temperatures of 80-100-120-140-160 °C are used separately. Calcite was the mineral which changes was observed through time. Minimum of 8 hours of reaction time is used to assess the mineralogical changes in shale samples. Changes in the Raman spectroscopy which are taken in certain intervals in 8 hours are used to see how mineralogy and organics changed in the powdered shale.