The Mount Simon formation in the Midwest region of the U.S. is considered as a potential candidate host reservoir for carbon storage. Obtaining knowledge of possible geochemically induced changes to the permeability and porosity of host CO2 storage sandstone will enable us to gain a deeper insight of the long-term reservoir behavior under the CO2 storage conditions. An experimental study of the interaction of CO2/brine/rock on saline formations in a static system under CO2 storage conditions was conducted. Chemical interactions in the Mount Simon sandstone resulting from exposure to CO2 and brine under sequestration conditions were studied. Samples were exposed to the simulated in-situ reaction conditions for six months. Two core samples of Mount Simon sandstone were used (one taken parallel to the bedding plane and the other perpendicular to the bedding plane). Core samples were exposed to a synthesized solution based on a typical Illinois Basin brine composition at a temperature of 85 °C and CO2 pressure of 23.8 MPa. Computed tomography (CT), x-ray diffraction (XRD), scanning electron microscopy (SEM), brine composition, core porosity, and core permeability analyses were conducted prior to and after the exposure experiments. The permeability and porosity measurements obtained from the sandstone sample showed a decrease after the core was exposed to CO2-saturated brine for six months. In addition, the permeability obtained from the core orientated parallel to the bedding plane is much larger than that measured from the core orientated perpendicular to the bedding plane. The combination of mineral dissolution and mineral precipitation occurring in the sample pores and cracks resulted in a net effect of blocking of flow which resulted in the observed decrease in permeability. This observation suggests that mineral dissolution and mineral precipitation could occur in the host deposit altering its characteristics for CO2 storage over time.
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