Unconventional Hydrocarbon Extraction from Geologic Formations with Carbon Storage Potential

Hydrocarbons from unconventional reservoirs such as shale account for an increasing fraction of the global energy portfolio. The current water-intensive hydrofracking technology for hydrocarbon extraction from shale-bearing reservoirs has limited efficiency and is environmentally unsustainable in the long run. Therefore, the use of CO₂ as an alternative fracking fluid has been proposed because it can penetrate into smaller pore spaces, and in the presence of water, CO₂ can react with shales to produce various chemical and morphological changes in these rocks. The fundamental mechanisms of shale-scCO₂-water interactions are investigated in this study. In this study, the chemical and morphological changes in shales with varying compositions of carbonates, clays, and quartz are investigated at elevated temperatures (T_max = 90 ^oC) and pressures (P_{CO2, max} = 150 atm). Since the pore spaces in shales are to the order of a few nanometers, synchrotron techniques at Argonne National Laboratory—including Ultra Small Angle X-Ray Scattering and Small Angle Scattering (USAXS and SAXS)—were performed to determine the changes in the pore spaces. The morphological changes were identified using X-Ray Microtomography. Changes in the phases were also determined using Thermogravimetric Analysis (TGA) and X-Ray Diffraction (XRD). Our studies showed that CO₂ reacts with shales in the presence of varying levels of water, produces significant increases in the pore spaces and effectively disorders the structure of shales. While, the clay phases in shales were disordered in the presence of scCO₂ and water, the carbonate and quartz phases remained relatively unchanged.