Presentation 2024-001
| Author(s) | Date | 2024-01-22 |
The Basal Cambrian Sandstone (BCS), 40-80 m thick at burial depths of 1000-3600 m has become the focus of increasing Carbon Capture and Sequestration (CCS) efforts in western Canada. Shell’s Quest facility, for example, has sequestered >7 Mt of CO2 in the BCS. To address a paucity of data on the unit’s characterization, twenty-eight cores have been investigated and provide new data from which a regional stratigraphic and diagenetic framework can be developed with direct implications for characterization and modeling of its properties.
Four facies associations consisting of fourteen distinct facies indicate the presence of 1) open-marine, 2) deltaic, 3) terrigenous continental, and 4) tidally-dominated subtidal depositional systems on a regionally extensive shelf. Stacking patterns in the BCS have been interpreted to record three regionally mappable transgressions, each demarcated by a flooding surface. BCS deposition terminates with a large maximum flooding surface (MFSx) that deposits fully marine offshore mudstone atop of marginal-marine tidally-influenced strata.
Burial diagenesis of the BCS and the associated impacts on porosity and permeability has been evaluated from core data. Interstitial clay and silt were found to be a critical control on permeability and even a 2-3% increase in clay content has been found to reduce vertical and horizontal permeability by three orders of magnitude, even in coarse-grained sediments. Additionally, evidence for secondary porosity is observed in abundant leached quartz grains suggesting the circulation of highly alkaline fluids. Petrographic and XRD results show that cements, mechanical and chemical compaction, and grain size sorting play a significant role in controlling the distribution of porosity and permeability. A better understanding of these relationships is critical to understanding injectivity of the formation and should be incorporated in associated geological models.
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