Assessing the impact of dip angle on carbon storage in saline reservoirs to aid site selection

Abstract

Reservoir dip angle and permeability significantly impact CO₂ plume migration and the amount of secondary phase trapping in storage formations. There is a fundamental trade-off between up-dip plume migration and secondary trapping that can be advantageous, or disadvantageous, for selecting an optimal CO₂ storage site. For example, low permeability reservoirs have limited plume migration up-dip, consequently, residual and solubility trapping are also limited. On the contrary, for highly permeable reservoirs, up-dip migration can be fast and extensive, leading to accelerated residual and solubility trapping. By performing a systematic simulation study of plume migration and secondary trapping in reservoirs with a range of permeabilities and dip angles, we found that having a dip angle of at least 1° and permeability of at least 500mD results in up to 88% of the plume being immobilized 100 years post-injection. In reservoirs with a permeability of at least 500mD, we can optimize the amount of immobilized CO₂ while limiting the amount of plume migration. As reservoir dip angles increase up to 2° and permeability increases, CO₂ plume migration increases progressively, and up to 8x more mass of CO₂ can migrate up-dip versus down-dip. At the same time, CO₂ solubility in brine and residual trapping work to decrease the plume volume and can immobilize 28% to 90% of the CO₂ plume over 100 years post-injection. Five influential parameters were identified that strongly influence the plume volume during the post-injection period for these dipping reservoirs: CO₂ saturation, residual gas saturation, CO₂ solubility in brine, CO₂ density, and formation permeability. We also investigated the impact of simulation grid resolution, the maximum non-wetting phase saturation, and the pore-size distribution parameter on predicted plume behavior. This work provides simple, reliable relationships between key site screening metrics, reservoir dip angle, and permeability to inform the site selection process and monitoring, measurement, and verification (MMV) design.