Pore-to-Core-Scale Network Modelling of $$\mathbf{CO}_{\mathbf{2}}$$ CO 2 Migration in Porous Media

Abstract

Pore network modelling offers a versatile and efficient means for examining the complex interplay of a variety of microscopic processes affecting subsurface migration of $$\hbox {CO}_{2}$$ injected for storage. We present a dynamic pore-to-core network model capable of simulating the full range of $$\hbox {CO}_{2}$$ migration processes under the influence of capillary and gravity forces, including $$\hbox {CO}_{2}$$ dissolution in brine. A parametric sensitivity study investigating four variables that define the microscopic Bond number, viz: mean pore radius, $$\hbox {CO}_{2}$$ –brine interfacial tension, brine– $$\hbox {CO}_{2}$$ density difference, and network height, was performed. Two broad classes of behaviours were identified—one quasi-stable and the other unstable (migratory)—and critical gas saturation $$({S}_\mathrm{gc})$$ was found to change in a non-monotonic way with transition from quasi-stable to migratory regime. The model predicts strong effects of gravity at the scale typical of continuum-type simulator gridblocks, and pore size distribution variance and pore connectivity were found to have a major impact on $${S}_\mathrm{gc}$$ which cannot be predicted a priori through the use of Bond number scaling. For temperatures and pressures above the $$\hbox {CO}_{2}$$ critical point, $$\hbox {CO}_{2}$$ and $$\hbox {CH}_{4}$$ flow regimes in brine displayed generally similar characteristics, suggesting that flow coefficients (e.g. relative permeability) of $$\hbox {CH}_{4}$$ and $$\hbox {CO}_{2}$$ in brine could be used interchangeably in continuum-type simulators with effectively the same results.