An Experimental Investigation of Three-Phase Flow of Water-Oil-Gas Mixtures Through Water-Wet Sandstones

Abstract

Three-phase relative permeabilities to water-oil-gas mixtures have been measured both under unsteady- and steady-state conditions through fired Berea sandstone. A computer-based photometric device was used for monitoring fractional flow of displacement fluids. An extension of the Welge-JPN method to three-phase flow was used for the calculation of relative permeabilities from displacement data. Several saturation histories relevant to petroleum reservoir exploitation were examined. Steady-state measurements with saturation histories similar to those in the unsteady-state experiments were made on the same core to enable comparison of the results. Water relative permeabilities were found to depend only on water saturation and were practically independent of the saturation histories considered. Gas relative permeabilities depended on the total liquid saturation; the components of the liquid being of no concern. They depended strongly, however, on the direction of saturation change of the gas phase. Oil relative permeabilities seemed to depend on saturations of all the phases present. Although the direction of oil and water saturation change phases present. Although the direction of oil and water saturation change did not influence oil relative permeabilities significantly, the decreasing gas saturation resulted in higher values as compared to those when the gas saturation was increasing. This seems to suggest that trapping of gas facilitates more free movement of oil. Predictions made by the use of Stone's two models yielded lower values of relative permeability to oil when compared to the experimental results, suggesting the inadequacy of these models even for the strongly water-wet rocks used in the present study. Steady-state measurements of three-phase relative permeability yielded results similar to those obtained by the displacement method for both oil and water. However, owing to a different trapping mechanism, gas phase relative permeability showed a much weaker dependence on the direction of gas saturation change under steady-state conditions when compared to the displacement process. Introduction There are several situations of practical importance in the exploitation of petroleum reservoirs where simultaneous flow of water-oil-gas mixtures is encountered. Waterflooding with free gas present because of prior production by solution gas drive or gas cap expansion drive, alternate water/gas drive, and gas drive with edge-water or aquifer encroachment are but a few examples of this phenomenon. Enhanced recovery methods such as thermal recovery or carbon dioxide immiscible displacement also generate simultaneous flow of three fluid phases. In short, three-phase flow is encountered often enough to warrant a detailed study of the process. Unfortunately, only a few scattered experimental studies have been reported in the literature starting with the one by Leverett and Lewis in 1941, who measured three-phase relative permeabilities in unconsolidated sands by a steady-state dynamic method. Table 1 summarizes, in chronological order, all the experiments reported to date. A detailed account of a literature search is available in another PRI report. As is evident from Table 1, different workers found the three relative permeabilities to depend differently on various fluid saturations. permeabilities to depend differently on various fluid saturations. Donaldson and Kayser have compared the magnitudes of relative permeabilities reported by various workers for water-wet systems and found permeabilities reported by various workers for water-wet systems and found them to deviate from one another so widely that none could be used with confidence in engineering calculations. In the absence of reliable experimental data, reservoir engineers have used theoretical models which make use of such information as capillary pressure or two-phase relative permeabilities to predict three-phase flow pressure or two-phase relative permeabilities to predict three-phase flow behavior. Stone's models which rely on two sets of two-phase data to predict three-phase relative permeabilities, have probably been used most predict three-phase relative permeabilities, have probably been used most widely, but their accuracy of prediction has never been established extensively.

Comparison of the three-phase oil relative permeability models

“…Saraf, Batycky, Jackson, and Fisher, 1982 [28] measured three-phase oil (soltrol), water (distilled water), and gas (nitrogen) relative permeabilities on Berea sandstone using both steady-state and unsteady-state methods. The threephase relative permeabilities were measured for several saturation directions (Sw+So~SgT, Sw-..-~So~Sg+, Sw~So~Sg~).…”

“…The models were tested against experimental data of Corey et al [8], Dalton et al [9], Saraf and Fatt [29], Holmgren and Morse [16], Schneider and Owens [32], and Saraf et al [28]. Fayers and Matthews [15] concluded that the normalized forms of Stone's Models I and II give very similar results when oil saturations are large, but differ considerably as residual oil saturation is approached.…”

Literature review and recommendation of methods for measuring relative permeability of anhydrite from the Salado Formation at the Waste Isolation Pilot Plant

“…The remainder of the apparatus was quite simple, especially as compared to that shown in Figures D-2 and D-3. In the apparatus of Figure D-2, the levels of oil and water in the fluid separator are monitored using an optical device (Saraf et al, 1982). As shown in Figure D The apparatus shown in Figure D-4, used by Gash (1 99 1) for measuring gas-brine relative permeabilities in coal samples, is as simple in principle as that used by Owens et al in 1956. Rather than measure produced liquids by visual observations of fluid levels, Gash weighed the produced liquids with an electronic balance, and he monitored the gas production with mass flow meters rather than by liquid displacement from a graduated cylinder.…”

A New X-Ray Absorption Method for Measurement of Three-Phase Relative Permeability

“…One recent application of the latter method to a three-phase system is given by Saraf et at. 2 Steadystate measurements, however, are difficult to carry out with precision with this method. In many cases, large volumes of injected and produced fluids, as well as line and end volumes, must be accounted for to obtain saturation changes at each point.…”

“…The present method uses (I) dual X-ray tracers, one dissolved in water and the other in oil, to discriminate between the absorption caused by these phases; (2) an iodine filter to eliminate polychromatic effects on relationships between saturation and absorption, thus simplifying calibration; and (3) dual X-ray data-measuring devices to obtain absorption data at two wavelengths simultaneously with a single X-ray beam generated at a selected tube potential. These improvements make it possible to analyze the movement of flood fronts in the presence of oil, water, and gas or to investigate the saturation distribution at unsteady state.…”