Experimental measurement of dynamic effect in capillary pressure relationship for two-phase flow in weakly layered porous media

Well-defined laboratory experiments have been conducted to determine the significance of dynamic effect in capillary pressure relationships for two-phase flow in weakly heterogeneous (layered) porous media. The heterogeneous layers are composed of a fine sand layer sandwiched between two coarse sand layers. Dynamic and quasi-static capillary pressure-saturation (P-S) and ∂S/∂t-t relationships are determined, which are then used to determine the dynamic effect, indicated by a dynamic coefficient (τ). As well known, τ establishes the speed at which flow equilibrium (∂S/∂t = 0) is reached. In consistent with previous studies, τ is found to be a nonlinear function of saturation that depends on the medium permeability and the intensity of heterogeneity. τ values increase in the regions of less permeability (fine sand) in the domain. However, the τ-S functional dependence follows similar trends at different locations within the domain including regions of different permeability. We argue that saturation weighted average of local τ-S curves can be used as an effective τ-S curve for the whole domain which, when done, follows an exponential trend too. The effective τ-S curves suggest that the effective τ values for the porous layers lie between the τ values of coarse and fine sands at the same water saturation, and it is dominated by the τ values of coarse sand as it occupied the maximum volume of the domain. © 2012 American Institute of Chemical Engineers