Two-dimensional reactive transport modeling of CO₂ injection in a saline aquifer at the Sleipner site, North Sea

Abstract

This paper presents a 2D reactive transport model of long-term geological storage of carbon dioxide. A data set from the Utsira formation in Sleipner (North Sea) is utilized for geochemical simulation, while the aquifer is approximated as a 2D cylindrically symmetric system. Using the reactive transport code TOUGHREACT, a 25 year injection scenario followed by a 10,000 year storage period are simulated. Supercritical CO₂ migration, dissolution of the CO₂ in the brine, and geochemical reactions with the host rock are considered in the model. Two mineralogical assemblages are considered in the Utsira formation, a sand formation that is highly permeable and a shale formation representing four semi-permeable layers in the system that reduce the upward migration of the supercritical CO₂. The impacts of mineral dissolution and precipitation on porosity are calculated. Furthermore, the 2D cylindrical geometry of the mesh allows simulating both the upward migration of the supercritical gas bubble as well as the downward migration of the brine containing dissolved CO₂. A mass balance of the CO₂ stored in, respectively, the supercritical phase, dissolved in the aqueous phase, and sequestered in solid mineral phases (carbonate precipitation) is calculated over time. Simulations with lower residual gas saturation and with different mesh refinement are also performed to test the sensitivity on mass balance estimates.