Unconventional formations of Western Canada and their potential for geological carbon storage

The Western Canada Sedimentary Basin (WCSB) hosts numerous fine-grained and tight stratigraphic units that are both prolific hydrocarbon unconventional reservoirs and potential targets for long-term CO 2 storage. However, their geological complexity poses significant challenges for predictive modeling. This paper reviews the depositional history, facies architecture, thermal maturity, total organic carbon (TOC), and mineralogy of four major unconventional formations of the WCSB, namely the Bakken, Duvernay, Horn River, and Montney, and evaluates how these characteristics influence the modeling of CO 2 injection and storage. Cross-formation comparisons show that siltstone- and tight-sandstone-dominated facies, such as the Middle Bakken Member and Montney turbiditic beds, generally provide higher injectivity at a given porosity, whereas organic-rich mudstone and shale facies, such as those in the Duvernay and Horn River, provide higher adsorption capacity but typically require fracture networks to access storage effectively. Thermal maturity patterns explain the distribution of oil, condensate, and dry gas, thereby controlling the dominant CO 2 storage mechanisms: oil-window and liquids-rich intervals, including the Bakken and parts of the Montney, favor miscible or near-miscible displacement, oil swelling, viscosity reduction, and dissolution, whereas dry-gas windows, particularly the Horn River and dry-gas domains of the Duvernay and Montney, favor sorption, gas displacement, and fracture-controlled flow. Mineralogical heterogeneity, particularly variations in silica, carbonate, and clay contents, and early diagenetic cementation, is identified as a key control on fracability, geomechanics, and reactive behavior during CO 2 exposure. Based on these findings, the paper proposes practical modeling guidelines, including facies-based property models with directional permeability tensors, compositional fluids conditioned to maturity, TOC-dependent sorption terms, and mineralogy-informed geomechanics and reactive-transport treatments. Remaining challenges and priorities for future research include multiscale upscaling, multicomponent adsorption measurement, and carbonate reactivity, all of which are critical for improving prediction of CO 2 storage performance in unconventional reservoirs.