The Effect Of Alcohol On Surfactant Mass Transfer Across The Oil/Brine Interface And Related Phenomena

Abstract

ABSTRACT The effect of alcohol on surfactant mass transfer from bulk solution to the oil/dilute tnicellar solution interface was studied. Various interfacial properties of the surfactant solutions and their ability for displacing oil were determined. For the surfactant-oil-brine systems studied, the interfacial tension (IFT) and surfactant partition coefficient did not change when isobutanol was added to the following systems: 0.1% TRS 10–410 in 1.5% NaCl vs n-dodecane and 0.05% TRS 10–80 in 1.0% NaCl vs n-octane. On the other hand, the interfacial viscosity, oil drop flattening time (i.e. the time required for an oil droplet to flatten out after being deposited on the underside of a polished quartz plate submerged in the micellar solution) and oil displacement efficiency were influenced markedly by the addition of alcohol. In the presence of isobutanol, the oil/dilute micellar solution interface became more fluid and the flattening time decreased from 90 seconds to less than a second or 420 seconds to less than a second, and the final oil saturation decreased from 30% to 5.36% and 11.73% to 1.28% respectively for the two systems mentioned above. Furthermore, it was observed that after the arrival of the oil bank, the ΔP leveled off for the isobutanol containing systems, whereas it continuously increased for the systems without isobutanol. This observation is consistent with the proposed role of alcohol in lowering the interfacial viscosity and promoting coalescence of oil ganglia in porous media. The flattening time was strikingly lower for the surfactant + alcohol system as compared to the flattening times in the presence of the surfactant or alcohol alone in the brine, suggesting that the rate of achieving ultra low IFT at the oil/micellar solution interface is strikingly enhanced by the presence of isobutanol resulting in greater oil recovery. In order to delineate the effect of surfactant mass transfer on in situ behavior of oil ganglia, we carried out several oil displacement experiments using equilibrated and nonequilibrated oil/micellar solution systems. For equilibrated systems, the oil displacement efficiency showed an excellent correlation with IFT and capillary number. However, for unequilibrated systems, the oil displacement efficiency depended on salinity. Below optimal salinity, the oil displacement efficiency almost remained the same for both equilibrated and nonequilibrated systems, whereas at and above optimal salinity the oil displacement efficiency was higher for non-equilibrated systems as compared to equilibrated systems. This was attributed to mass transfer rate effects in these systems. Both sand packs-and Berea cores gave similar results. The results of this study demonstrate the importance of transient phenomena at oil/dilute micellar solution interface for oil displacement process with emphasis on the effect of alcohol and salinity.