The Impact of Pore-Scale Flow Regimes on Upscaling of Immiscible Two-Phase Flow in Geothermal Reservoirs

Abstract

Two-phase flow conditions are frequently encountered in geothermal reservoirs due to gradients in pressure and temperature. Since empirical or theoretical extensions of Darcy's law for immiscible two-phase flow have shown significant limitations in properly modelling flow at the continuum-scale, in this paper we start with the upscaled equations based on pore-scale flow regimes (i.e., the topology of flowing phases) recently developed by Picchi and Battiato (2018) to understand the impact that the topology of flowing phases may have on relative permeability estimates at geothermal reservoir conditions. We illustrate and quantify the effect of pore-scale flow regimes on relative permeability by focusing on core-annular and plug flow regimes in a capillary tube, as surrogates of the large- and small-ganglion dynamical regimes, respectively. We show that, for cases with lower viscosity ratios, typical of geothermal systems, differences in the relative permeability between plug and core-annular flows is considerable in the whole range of saturation and reaches peaks larger than 100% with respect the relative permeability computed for core-annular flow.