Regular Article

The correlation of the steady-state gas/water relative permeabilities of porous media with gas and water capillary numbers

Foundation for Research and Technology Hellas – Institute of Chemical Engineering Sciences, Stadiou Street, Platani, 26504 Patras, Greece

^* Corresponding author: ctsakir@iceht.forth.gr

Received: 2 February 2018
Accepted: 18 March 2019

Abstract

The steady-state gas, k _rg, and water, k _rw, relative permeabilities are measured with experiments of the simultaneous flow, at varying flow rates, of nitrogen and brine (aqueous solution of NaCl brine) on a homogeneous sand column. Two differential pressure transducers are used to measure the pressure drop across each phase, and six ring electrodes are used to measure the electrical resistance across five segments of the sand column. The electrical resistances are converted to water saturations with the aid of the Archie equation for resistivity index. Both k _rw and k _rg are regarded as power functions of water, Ca_w, and gas, Ca_g, capillary numbers, the exponents of which are estimated with non-linear fitting to the experimental datasets. An analogous power law is used to express water saturation as a function of Ca_w, and Ca_g. In agreement to earlier studies, it seems that the two-phase flow regime is dominated by connected pathway flow and disconnected ganglia dynamics for the wetting fluid (brine), and only disconnected ganglia dynamics for the non-wetting fluid (gas). The water saturation is insensitive to changes of water and gas capillary numbers. Each relative permeability is affected by both water and gas capillary numbers, with the water relative permeability being a strong function of water capillary number and gas relative permeability depending strongly on the gas capillary number. The slope of the water relative permeability curve for a gas/water system is much higher than that of an oil/water system, and the slope of the gas relative permeability is lower than that of an oil/water system.