MINERALOGICAL CHARACTERIZATION OF THE WEYBURN RESERVOIR, SASKATCHEWAN, CANADA: ARE MINERAL REACTIONS DRIVING INJECTED CO_2 STORAGE?

摘要

Water-rock reactions are critical to the short- and long-term storage of injected CO_2. Carbonate-CO_2-fluid reactions release carbon while silicate-CO_2-fluid reactions potentially store CO_2 in the fluid and as newly formed carbonates. The detailed mineralogy of the Weyburn reservoir, with particular attention paid to EnCana's flow unit nomenclature, is described. Mineral reaction modelers, assessing the long-term fate of injected anthropogenic CO_2, will use the mineral modes of flow units as input variables. LPNORM analysis established the presence and abundances of minerals in each reservoir flow unit. Midale Evaporite "Three Fingers Zone" (TFZ), Midale Marly, and Frobisher Marly are comprised of finely crystalline dolomite, minor calcite and anhydrite, and up to 35 wt% silicate minerals. The uppermost Midale Marly and the TFZ are the intervals where the greatest volume of reactive silicate minerals is found. Marly and TFZ porosity is generally submicroscopic, with little pore filling mineralization. Midale Vuggy shoal and intershoal flow units are dominantly calcite with relatively low ( < 10 wt%) silicate mineral abundances. Potentially reactive silicate minerals, such as illite and feldspar are in short supply throughout the reservoir, averaging 4 wt% and 1 wt%, respectively. Vuggy flow units are characterized by variable pore sizes (up to 2 mm long) that are most commonly filled with carbonate and anhydrite. Anhydrite cementation and anhydrite replacement of microcrystalline calcite is more common toward the erosional contact above the Frobisher beds. The mineralogical normative results show that even in a carbonate reservoir such as at Weyburn, silicate minerals are present to potentially react with CO_2-charged fluid. Given the quantitative mineral norms, known reservoir properties, no CO_2 leakage, and sufficient time (i.e. 5000 years), mineral reactions and solubility and ionic trapping could store up to 45 million metric tonnes of CO_2.