Petrography, Petrophysics, and Pore Systems of Cambrian Sandstones and Dolomites in Southwestern Ontario: Implications for Carbon Capture and Storage

This paper investigates relationships between lithology and pore systems in Cambrian deposits of southwestern Ontario, a current carbon capture and storage target. I integrate SEM imagery that includes elemental mapping, with optical petrography, X-ray diffraction results, and data from routine core analysis on samples from a single well that penetrates the entire approximately 100 m-thick section. The rocks comprise a range of lithologies, including sandstones, dolomitic sandstones, sandy dolomites, and dolomites. Most of the sandstones are arkosic, with potassium feldspar contents that can be >50%. Highest porosity (>20%) is found in sandstones and lowest (<1%) is in the dolomites. Sandstones can have permeability >100 mD, whereas the tightest dolomites have permeability in the 10s of μD range. Three main pore types are present: intergranular, intragranular, and vugs. The first two are present in sandstones and the vugs are present in dolomites. Intragranular porosity is primarily in orthoclase feldspar grains, where diagenesis removed grain centers, effectively leaving no alteration products. The results are significant because they demonstrate the arkosic nature of some Cambrian sandstones, show that feldspar content is a significant control on porosity, and that future petrophysical analyses need to be calibrated using quantitative mineralogy data. Wireline log and core data presented herein are derived from a single well but integration of these data with results of previous mapping suggests they are likely to be representative of the Cambrian section throughout much of the subsurface of southwestern Ontario.