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 degrees F [21 degrees C]. Individual relative permeability curves obtained as a function of gas saturation approach the 45 degrees [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 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 thatthe curvatures of the relative permeability curves diminish as the IFT is reduced.the irreducible gas and liquid saturations approach zero as the IFT approaches zero, andrelative gas/oil permeabilities for gas-condensate reservoirs are altered from the normal relative permeabilities only at pressures, temperatures, and compositions close to permeabilities only at pressures, temperatures, and compositions close to the critical point. Introduction IFT, through capillary forces, plays an important role in determining the flow behavior of hydrocarbon fluids in porous rocks. Petroleum engineers involved in EOR are using chemicals, mainly Petroleum engineers involved in EOR are using chemicals, mainly surfactants, to lower the IFT between oil and water in oil reservoirs. As a result of alterations in the IFT, the flow characteristics will be changed. Consequently, the relative permeabilities to both phases will be affected. IFT's also approach zero at the critical point for hydrocarbon systems. This could be important in two-phase flow point for hydrocarbon systems. This could be important in two-phase flow in condensate reservoirs. Many factors affect relative permeability data. Most of the literature concerning relative permeabilities states that they are functions of only saturation, saturation history, rock wettability, and pore-size distribution. Some authors have suggested that water/oil pore-size distribution. Some authors have suggested that water/oil viscosity ratio can also affect relative permeabilities. Although it has been known for some time that low IFT's could reduce residual oil, only recently has the effect of IFT on the relative permeability of hydrocarbon fluid systems been investigated. Therefore, the primary objective of this work is to study the influence of IFT on primary objective of this work is to study the influence of IFT on the relative permeability of a binary hydrocarbon system: namely. methane/propane mixtures. The research is an extension of studies initiated by Saeidi and Handy. The methane/propane system is representative of an idealized gas-condensate system. The liquid phase can reasonably be assumed to be the wetting phase. The phase can reasonably be assumed to be the wetting phase. The results obtained in this work with methane and propane clearly indicate that gas/oil relative permeability data are strong functions of both saturation and IFT. Low IFT's were obtained by conducting the experiments near the critical point of the hydrocarbon fluid system. The experiments were carried out using Berea sandstone at a constant temperature of 70 degrees F [21 degrees C]. On the basis of the phase behavior of the methane/propane system, a new experimental technique was developed to obtain individual relative permeabilities to gas and oil. Bardon and Longeron have discussed a procedure for obtaining gas/oil relative permeability ratios for two-component hydrocarbon systems near the permeability ratios for two-component hydrocarbon systems near the critical point. Wagner and Leach studied the effect of displacement efficiency as a function of IFT under similar conditions. In both papers, relative permeability data were obtained by unsteady-state papers, relative permeability data were obtained by unsteady-state methods. With our procedure, the methane/propane mixtures are initially at a pressure and temperature such that they are in the one-phase region on the pressure/composition phase diagram. As fluids are transferred into the core, the pressure is dropped through a needle valve to a predetermined level in the two-phase region. A differential pressure is imposed to create flow and to enable measurement of the required data. This procedure gives a steady-state measurement of relative permeabilities. It should be pointed out that liquid saturation can be built up from zero, which is the direction in which saturations would change when a gas-condensate reservoir is produced. If the propane concentrations are higher, however, the system will be initially 100% liquid saturated. In this case, the method gives drainage (decreasing wetting-phase saturation) rather than imbibition (increasing wetting-phase saturation) relative permeability data. IFT for a two-phase, two-component system approaches zero as the system approaches the critical point. For any two-component system, such as methane/propane, the IFT between the two phases is a function of only composition and pressure, provided that the temperature remains constant. In this work. relative permeabilities to gas and oil were obtained at different IFT levels by permeabilities to gas and oil were obtained at different IFT levels by changing the composition or the pressure of the experiment near the critical region of the methane/propane system. Possible effects on the phase behavior of gas condensates as a result of the presence of porous media were investigated. The literature on this subject is contradictory but the results obtained seem to lend support to results reported by Sigmund et al.; namely, that the porous medium has little or no effect on the equilibrium phase behavior. phase behavior. Hysteresis effect on the relative permeability (drainage and imbibition) were also investigated, though not extensively. Relative permeability data for the gas-condensate systems were compared permeability data for the gas-condensate systems were compared with conventional Welge-type experimental relative permeability with kerosene and nitrogen as the flowing fluids. SPERE P. 257