Water-Carbon Dioxide-Rock Interactions at the Pembina Cardium Carbon Dioxide Monitoring Pilot

The results of an investigation of the impact of injected CO2 on reservoir mineralogy and formation water composition at the Pembina Cardium CO2 Monitoring Pilot in Alberta, Canada are presented. Carbon dioxide injection at the pilot is primarily into the upper two of three stacked sandstone units of the Cardium Formation. Samples of the reservoir rock were recovered immediately before and two years after the initiation of CO2 injection. The physical, chemical and mineralogical compositions of the core samples analyzed were similar, irrespective of when the core was recovered. Attributing dissolution features in post-CO2 flood core to the interaction of minerals and carbonic acid was problematic due to the existence of preexisting dissolution features related to formation diagenesis. No new mineral phases were observed in any of the post-CO 2 flood core analyzed.;Samples of co-produced water and gas were collected from the eight production wells at the pilot site immediately before, and for a period of 22 months following the initiation of CO injection. Significant increases in produced CO2 following the initiation of CO2 injection were observed at four of the eight wells monitored. Changes in the water chemistry, including a decrease in pH and an increase in dissolved solids (e.g. Ca2+, Fe2+ and HCO32-) were observed at each of the same 3 four wells. At least some of the observed changes can be attributed to carbonate cement (i.e., calcite and siderite) dissolution. Additional changes in water composition may be due to the corrosion of production tubing and/or the exchange or desorption of metallic cations from the surface of the clay minerals and/or organic matter present in the formation.