Hydro-mechanical-chemical modeling of sub-nanopore capillary-confinement on CO₂-CCUS-EOR

Nanopore/subnanopore networks comprising tight reservoirs exhibit special behaviors in the storage and transport of capillary-confined fluids. We develop a hydro-mechanical-chemical model coupling the response of capillary-confined phase behavior, multicomponent flow, reservoir deformation and reaction-controlled porosity evolution to explore the effect of nanopore confinement on enhanced oil recovery and CO₂ storage. The results reveal that confinement effects change both in chemical potential and isothermal compressibility of individual components and thus increases volume expansion for any given pressure drop. For constrained mixtures, the CO₂ K-value (at fixed pressure) and the MMP(at fixed aperture) will shift to smaller than the bulk state. Moreover, capillary-confinement causes an increased production of heavier components when reservoir pressure is below MMP and a higher production of all components and a smaller reservoir inflation when reservoir pressure is higher than MMP - where miscibility dominates. Meanwhile, capillary-confinement causes a slight increase in CO₂ retention rate in the calculation for two cases of native oils with contrasting light oil fractions but in identical reservoirs. Thus any production strategy for a combined CO₂ capture and storage (CCS) operation needs to be formulated in full consideration of the rock and fluid properties for each potential site.