A Numerical Simulation Framework for the Design, Management and Optimization of CO2 Sequestration in Subsurface Formations

The overall objective of the project is the development of a numerical framework for the simulation of subsurface CO2 sequestration processes. The following important research areas were pursued simultaneously during this three-year GCEP project: (1) accurate modeling of CO2 trapping by dissolution and residual trapping, (2) analysis and construction of consistent and high-order adaptive implicit discretization schemes, (3) development of an adaptive multiscale finite-volume formulation for nonlinear multiphase flow and transport, (4) development of a stochastic framework for constructing Darcy-scale CO2 transport equations that are consistent with the pore scale physics, and (5) extension of GPRS (General-Purpose Research Simulator) for modeling chemical reactions coupled with compositional flow and transport. Dissolution trapping is studied for a layer of super-critical CO2 that overlies a saline saturated porous medium in a structural trap. Dissolution of the CO2 into the underlying brine leads to a local density increase, and that results in buoyancy driven fingering. Stability analysis based on the dominant-mode of the self-similar diffusion operator resolves the critical time and wavelength associated with the onset of the instability quite accurately. The nonlinear evolution of the instability is analyzed using high-accuracy direct numerical simulation. The nonlinear solutions of the early time period show excellent agreement with the predictions from our linear-stability theory. At later times, macroscopic fingers display intense nonlinear interactions that significantly influence both the propagation speeds and the overall mixing rate. Analysis for typical aquifers shows that for a permeability variation of 1− 3000mD, the critical time can vary from 2000 yrs to about 10 days, while the critical wavelength varies from 200m to 0.3m. The behavior of CO2 gravity currents in sloping aquifers in the presence of residual trapping is investigated using a simple mathematical model that accounts for residual trapping in the wake of the migrating gravity current. The analysis provides insight into the length and time scales associated with the competition between up-dip migration of the current and residual trapping of the CO2 in its wake. The dependence of the max-