Influence of Interfacial Tension on Gas/Oil Relative Permeability in a Gas-Condensate System

Abstract

Summary To understand better the effect of interfacial tensions (IFT's) on gas/oil relative permeabilities, with particular emphasis on those effective in condensate reservoirs, an experimental procedure was developed and used with the highly volatile methane/propane system. The objective was to measure steady-state relative permeabilities as functions of IFT. Thus the IFT was varied from 0.03 to 0.82 dynes/cm [0.03 to 0.82 mN/m], corresponding to pressures near the critical at a constant temperature of 70°F [21°C]. Individual relative permeability curves obtained as a function of gas saturation approach the 45° [0.79-rad] diagonals for both gas and oil as the IFT is lowered. This supports the expectation that relative permeability curves for both gas and oil become straight lines as the IFT approaches zero. At the highest IFT for which experiments were performed (0.82 dynes/cm [0.82 mN/m]), the relative permeability curves approached those obtained for a nitrogen/kerosene flood for which the IFT is approximately 30 dynes/cm [30 mN/m]. The most important conclusions derived from this work are that (1) the curvatures of the relative permeability curves diminish as the IFT is reduced, (2) the irreducible gas and liquid saturations approach zero as the IFT approaches zero, and (3) relative gas/oil permeabilities for gas-condensate reservoirs are altered from the normal relative permeabilities only at pressures, temperatures, and compositions close to the critical point.