Dispersion, permeability heterogeneity, and viscous fingering: Acoustic experimental observations and particle-tracking simulations

Abstract

Stable and unstable displacement experiments were performed in millstone and limestone cores. Concentration histories at ten locations along the core samples were obtained by acoustic measurements. Particle-tracking simulations of the displacements were also made utilizing permeability distributions measured with a permeameter. The combination of experimental observations and simulations indicate that superstable (M<1) displacements suppress the influence of heterogeneity; this suppression was reflected in smaller apparent dispersivities as the mobility ratio decreased below unity. In the millstone, which exhibited random heterogeneity, two-dimensional particle-tracking simulations reproduce with reasonable accuracy the growth of the fingered region in unstable displacements. In homogeneous porous media, concentration histories obtained in three-dimensional simulations did not differ significantly from their two-dimensional counterparts. In the more heterogeneous limestone, unstable displacements accentuated the influence of heterogeneity leading to longer transition zones. Two distinct flow regimes were observed in unstable displacements: (1) an initial period of rapid transition zone growth and (2) a subsequent period in which leading and trailing edges of the transition zone travel at nearly constant velocities.