Assessing CO2 injection capacity and safe CO2 injection rates in the fractured tight Potsdam sandstone reservoir, St. Lawrence Platform, Quebec

CO 2 storage operations in fractured sandstone reservoirs are challenging as they may result in high reservoir pressure buildup, caprock hydraulic fracturing, or fault slip reactivation. We assess CO 2 injection capacity in fractured tight saline aquifer of the Lower Paleozoic Potsdam sandstone in the Bécancour fault block, St. Lawrence Platform at a depth of ∼1.2 km. Static storage capacity evaluation and 3D dynamic reservoir simulations of CO 2 injection in a vertical and a horizontal well are conducted. The fractured reservoir model is calibrated by performing a history match based on brine production. CO 2 is predominantly stored in the gas phase rather than dissolved in water, with a greater amount residing in the matrix than migrating through fractures. The pressure front propagates through the fractured reservoir much faster and farther than the CO 2 plume, elevating geomechanical and well integrity risks at a greater distance from the injection site area. In fractured tight reservoirs with pressure-limited capacity, CO 2 single-well accessible storage potential and actual injection rate are strongly controlled by pore volume, bottomhole pressure buildup, and well design. Utilization of horizontal, rather than vertical, wells in fractured tight reservoirs is estimated to be preferable for CO 2 injection as it helps to increase reservoir contact, maximize intersection with vertical fractures, reduce bottomhole pressure and vertical CO 2 plume propagation, lower the risk of caprock leakage and increase storage capacity. A grid-sensitivity test indicates that dynamic properties, such as pressure and saturation, depend on grid cell size and are more accurately estimated in fine resolution grids.