Impact of injection scheduling on CO2 migration and trapping efficiency in the Johansen formation

Injection scheduling is increasingly considered as an operational lever for optimizing carbon dioxide (CO2) storage in saline aquifers, yet its long-term impact on trapping efficiency at field scale remains uncertain. This study employs a field-calibrated vertical equilibrium model of the Johansen formation, offshore Norway, to compare four injection strategies: constant, ramped, pulsed, and low steady, under equal total injected mass. Simulations span 1000 years, including both injection and post-injection phases, to evaluate plume migration, bottom hole pressure (BHP) evolution, and partitioning among residual and solubility trapping. Results show that while injection schedule significantly influences short-term injectivity and peak BHP with differences up to 80 bar, its effect on millennial-scale trapping efficiency is negligible. By 1000 years, all scenarios converge to a similar distribution, with 57-58% dissolved in brine, 30-34% immobilized by residual trapping, and 8-9% persisting as a mobile plume, with inter-schedule differences less than 2% of the total injected mass. These findings indicate that, in a laterally open and well-connected aquifer such as Johansen, long-term storage security is governed primarily by reservoir properties and dissolution dynamics rather than by operational schedule. Consequently, injection scheduling should be regarded as a tool for short-term pressure management and infrastructure safety, not as a determinant of ultimate storage performance. This distinction provides practical guidance for designing CO2 storage projects and regulatory assessments of long-term containment.