A multi-scale approach for numerical modelling of the CO2 sequestration process

Abstract

Subsurface carbon dioxide (CO2) sequestration is a promising technology to reduce the CO2 emission into the atmosphere. After injection into subsurface formation, the carbon dioxide plume can migrate several kilometres until it is fully trapped. Four major mechanisms play an important role in trapping which include structural trapping, residual trapping, dissolution trapping or mineralization. The accurate numerical simulation of the sequestration process is challenging owing to the complexity of buoyancy driven enhanced dissolution and convective propagation of the CO2 plume. To resolve these processes, one often needs an extremely fine computational grid which makes the CPU time prohibitive for modelling at reservoir scale. Several simplified models were proposed which include analytical models (Hesse, 2008; Gasda et al., 2012), vertical equilibrium models (Gasda et al., 2012; (Pruess & Nordbotten, 2011) and an algebraic multi-scale model (Hesse, 2008).
Here we proposed and applied the multi-scale models with dissolution for modelling of CO2 sequestration on the large-scale. Several numerical experiments are considered using adjusted small-scale simulation of the plume dynamic in a sloped aquifer. The enhanced rate of dissolution captured in the small-scale models with geometrical properties was then applied to the simulation in the realistic aquifer. A sink term applied at the CO2-brine-interface is implemented in the ADGPRS program. This term numerically acts as the dissolution mass transfer that would otherwise occur in a compositional simulation at fine resolution.
It is important to contemplate the slow reduction in dissolution rate after the fingers begin to interact with the bottom of the reservoir. After interaction becomes significant, a reduction in the local dissolution rate is considered. We compared our multi-scale approach with a high-fidelity compositional simulation at high resolution, similar to the results presented in (Elenius, Voskov & Tchelepi, 2015). The applicability of the proposed approach was validated on the numerical model of a realistic aquifer.