A Pseudo‐Vertical Equilibrium Model for Slow Gravity Drainage Dynamics

Abstract

Vertical equilibrium (VE) models are computationally efficient and have been widely used for modeling fluid migration in the subsurface. However, they rely on the assumption of instant gravity segregation of the two fluid phases which may not be valid especially for systems that have very slow drainage at low wetting phase saturations. In these cases, the time scale for the wetting phase to reach vertical equilibrium can be several orders of magnitude larger than the time scale of interest, rendering conventional VE models unsuitable. Here we present a pseudo‐VE model that relaxes the assumption of instant segregation of the two fluid phases by applying a pseudo‐residual saturation inside the plume of the injected fluid that declines over time due to slow vertical drainage. This pseudo‐VE model is cast in a multiscale framework for vertically integrated models with the vertical drainage solved as a fine‐scale problem. Two types of fine‐scale models are developed for the vertical drainage, which lead to two pseudo‐VE models. Comparisons with a conventional VE model and a full multidimensional model show that the pseudo‐VE models have much wider applicability than the conventional VE model while maintaining the computational benefit of the conventional VE model.

Small-scale capillary heterogeneity linked to rapid plume migration during CO2 storage

“…Conventionally, the field-scale impact of capillary pressure has been evaluated without consideration of small-scale heterogeneities. In homogeneous reservoirs capillarity leads to an increase in the sweep of the plume and retardation of its lateral migration (Golding et al, 2013;Becker et al, 2017). We have shown that the presence of structured heterogeneities can lead to an outcome which has qualitatively the opposite impact.…”

An Adaptive Multiphysics Model Coupling Vertical Equilibrium and Full Multidimensions for Multiphase Flow in Porous Media

“…Vertical drainage in this state continues only at a very low rate and is not reproduced by the VE model, which assumes that no brine phase above residual saturation is held back in the gas plume. This could be improved by a pseudo‐VE model that assumes a pseudo‐residual brine phase saturation in the plume, which is higher than the residual saturation and reduced dynamically due to slow vertical drainage (Becker et al, ). We note that the full multidimensional model does not necessarily give better solutions in the VE subdomain.…”

Small‐Scale Capillary Heterogeneity Linked to Rapid Plume Migration During CO2 Storage

“…Conventionally, the field‐scale impact of capillary pressure has been evaluated without consideration of small‐scale heterogeneities. In homogeneous reservoirs capillarity leads to an increase in the sweep of the plume and retardation of its lateral migration (Becker et al, 2017; Golding et al, 2013). We have shown that the presence of structured heterogeneities can lead to an outcome which has qualitatively the opposite impact.…”

“…Conventionally, the field-scale impact of capillary pressure has been evaluated without consideration of small-scale heterogeneities. In homogeneous reservoirs capillarity leads to an increase in the sweep of the plume and retardation of its lateral migration (Becker et al, 2017;Golding et al, 2013). We have shown that the presence of structured heterogeneities can lead to an outcome which has qualitatively the opposite R 1 is the central vertical distance from the top of the plume to the caprock (initially ≈40 m from the top of the injection well to the caprock), and R 2 is the growing lateral extent of the plume directly under the caprock for x > 1,000 m, once the plume has reached the caprock.…”