Maziyar Nazemi

Underground geological storage of carbon dioxide (CO2) has emerged as one of the most viable solutions for mitigating global carbon emissions during the transition to a net-zero economy. Within subsurface geological strata, saline aquifers and depleted oil and gas reservoirs are the primary targets for CO2 storage. However, in regions with limited oil and gas production operations, underground storage is generally assumed to be non-viable or uneconomic even where potential storage capacity is present, and this assumption is further amplified in tectonically active regions. Herein, we review the characteristics of deep saline aquifers necessary for CO2 storage in tectonically active regions focusing on the Lower Mainland of British Columbia (LMBC), Canada. We discuss the subsurface and reservoir characteristics necessary for successful CO2 storage and summarize available information from the LMBC.
In the LMBC, conditions for underground storage of CO2 are favorable in some Tertiary strata below ~1,000–1,264 m depth, especially if in-situ or ex-situ CO2 dissolution is employed. Sandstone beds in Tertiary strata between 1,000 and 2,000 m have reservoir characteristics that are favorable for CO2-brine solution injection, including: permeability (0.1–2,390 mD), porosity (12–23% based on well logs and using a 9% cutoff; 2.4–22.3% measured in core samples), and salinity (751–37,438 ppm), and some sandstone beds show reasonable reservoir capacity (based on drill stem test results). Coal seams in Tertiary strata also have CO2 storage potential but require further study to quantify their potential. There are large regions of the LMBC where Tertiary strata are situated greater than 5 km and 10 km from mapped faults, and this lowers the potential risk of CO2-brine leakage.
There is limited data available for Upper Cretaceous strata below the LMBC, and hence, there is greater uncertainty in determining CO2 storage potential in these strata. Well-log-based porosity ranges from 12.5–20% (using a 9% porosity cutoff), which is favorable for CO2 storage. Available 2D seismic data shows that Upper Cretaceous rocks below the LMBC are heavily faulted, although many faults terminate at the top of the Upper Cretaceous interval. The distribution of faults increases the potential risk of CO2 leakage, although the confinement of faults to the Upper Cretaceous suggests the risk of leakage to surface or into shallow aquifers is minimal; this is especially true if in-situ or ex-situ CO2 dissolution is employed.