Wettability Versus Displacement in Water Flooding in Unconsolidated Sand Columns

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Abstract
Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 227–232. A series of water floods was made on laboratory prepared unconsolidated sand columns to study the effects on oil recovery of the solid-water-oil contact angle, the oil-water interfacial tension, flood rate, and oil viscosity. A procedure was developed for treating silica sand with silicone polymer to produce surfaces of varying degrees of wettability as evaluated by measuring the contact angle on a flat silica plate that had been simultaneously treated with the sand. Fluid interfacial tensions were changed by the use of surface active agents in the flood water. Water-wet, oil-wet, and intermediate wettability systems were studied at high and at low values of interfacial tension, at several flood rates, and with oils of different viscosities. For both oil-wet and water-wet systems and a low viscosity oil, recoveries were functions of the oil-water interfacial tension; also, increase in flood rate resulted in increased oil recoveries. High interfacial tension floods were more efficient than low interfacial tension floods on water-wet systems, while low interfacial tension floods were more efficient on oil-wet systems. Intermediate or neutral wettability systems were less sensitive to rate of flood advance and interfacial tension than either oil-wet or water-wet systems. The effects of surface forces on oil recovery for high viscosity oils were not so well defined as for low viscosity oils. Introduction: Reservoir rock surfaces vary in their wettability, some being water-wet while others are apparently oil-wet. The factor of wettability enters into reservoir performance in both primary and secondary recovery, and into laboratory measurements of capillary pressure, connate water saturation, and relative permeabilities. In theory, the degree of wettability is measured by the contact angle for the system solid-water-oil. A water-wet system is defined as one in which the advancing water contact angle is less than 90°. An oil-wet system is one in which the advancing water contact angle is greater than 90°.

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