PFLOTRAN: Massively Parallel 3D Simulator for CO2 Sequestration in Geologic Media

Geologic sequestration in depleted oil reservoirs, saline aquifers, etc. has been proposed as an effective way to stabilize the concentration of CO2 in the atmosphere and thus mitigate its effect on global climate change. We have developed a massively parallel 3-D reservoir simulator PFLOTRAN for modeling supercritical CO2 sequestration in geologic formations based on continuum scale mass and energy conservation equations. The simulator incorporates the effects of CO2 and H2O dissolution and diffusion in the aqueous and CO2-rich phases, respectively. The mass and energy equations are sequentially coupled to reactive transport equations describing multi-component chemical reactions within the formation including aqueous speciation and precipitation and dissolution of minerals, including CO2-bearing phases, to describe aqueous and mineral CO2 sequestration. The effect of injected CO2 on pH, CO2 concentration within the aqueous phase, mineral stability, and other factors can be evaluated with this model. The multiphase flow field is coupled to changes in porosity and permeability of the geologic porous medium caused by precipitation and dissolution reactions of minerals. Parallelization is carried out using the PETSc parallel library package based on MPI providing high parallel efficiency and allowing simulations with several tens of millions of degrees of freedom to be carried out—ideal for large-scale field applications involving multi-component chemistry. A lookup table provides rapid evaluation of the H2O and CO2 equations of state. Several examples are presented which examine the predicted distribution and fate of CO2 injected into a subsurface geologic system and evaluate the numerical efficiency of the simulator.