An investigation of the impact of injected CO2 on reservoir mineralogy was completed as part of the geochemical monitoring and modelling of the Pembina Cardium CO2 Monitoring Project southwest of Drayton Valley, Alberta, Canada. Oil production at the pilot is primarily from the upper two of three stacked sandstone units of the Cardium Formation in the Pembina field. Core analyzed included samples from each of the three sandstone units, and encompassed three distinct time periods: pre-water flood (1955), pre- CO2 flood (2005), and post- CO2 flood (2007). The results of whole rock analysis (XRF, ICP, and XRD), and microscopy (polarizing and electron microprobe) suggest the three separate sandstone units are both texturally and compositionally similar regardless of when the core was recovered. Framework grains are predominately sub-angular to sub-rounded quartz/chert (up to 90.0 wt%), and include smaller amounts of lithic fragments (shale), feldspar (k-feldspar, and albite), mica (muscovite and chlorite), and fluor-apatite. Authigenic pyrite is found as finely disseminated rhombs throughout the formation. Clay minerals present are predominantly kaolinite and illite. Kaolinite appears as fine discrete pore filling books, and is considered to be authigenic. Illite occurs as a major constituent of shale fragments, as well as fine pore bridging strands. The sandstone’s irregular pores are cemented to varying degrees by silica and/or carbonate minerals (calcite and siderite). Dissolution features associated with formation diagenesis, including the degradation of detrital grains (quartz and feldspar), the partial and/or complete removal of carbonate cements, and the presence of residual clays, are found in core from each of the three time periods. Attributing dissolution features in post- CO2 flood core to the interaction of minerals and carbonic acid is difficult due to the geologic history of the formation.