MICHAELS, A.S., MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS. MEMBER AIME STANCELL, ARNOLD, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS. PORTER, M.C., MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.
Abstract
Previous laboratory studies have demonstrated that the injection of small quantities of reverse wetting agents during water displacement can increase oil recovery from unconsolidated porous media. In the present investigation, an attempt has been made to determine more fully the effects of reverse wetting treatments and to clarify the mechanism by which increased oil recovery is effected Water-oil displacements were performed in beds of 140–200 mesh silica sand. Hexylamine slugs (injected after 0.25 pore volume of water through put), when adequate in size and concentration, were effective in promoting additional oil recovery. Their effectiveness increased with the quantity of amine injected. However, slugs of sufficient size and concentration to stimulate oil production at water flow rates of 34 ft/day did not do so at 4 ft/day.Visual studies in a glass grid micromodel have shown that the stimulation of oil production, via aqueous bexylamine, is a result of transient changes in the oil wettability of the pore walls. If the am in e slug is of sufficient size and concentration to induce significant changes in the adhesion-tension, large continuous oil masses will be formed. If the superficial water velocity is high enough to result in rapid desorption of the am in e, a favorable "wettability gradient" may be established across the masses; under such conditions, high oil mobility is observed, and increased oil recovery results.
Introduction
It is generally agreed that the efficiency of oil displacement by water in porous media is limited in part by capillary forces which cause the retention of isolated masses of oil - resulting in the so-called "irreducible minimum oil saturation". Recent estimates indicate that there are about 220 billion bbl of petroleum in United States reservoirs which are not economically recoverable with present techniques (such as water flooding). This amounts to almost five times the known recoverable reserves. It has been recognized for some time that a suitable alteration in the water-oil interfacial tension and/or the contact angle, as measured between the water-oil interface and the solid surface, should result in better displacement efficiency. Surface active agents can be used as interfacial tension depressants to accomplish this objective, but unfortunately, the additional oil recovery is seldom commensurate with the treatment cost.In contrast to interfacial tension depressants, the effect of contact angle alterations on water- oil displacements has received relatively little attention in the literature. It is known that the wettability affects the displacement process. Displacements in water-wet systems generally result in lower residual oil saturations than those in oil-wet systems. The effect of "transient" wettability alterations concurrent with the displacement process have been investigated by Wagner, Leach and coworkers, wherein it has been demonstrated that the establishment of water- wet conditions during water flooding of oil-wet, oil-saturated porous media is accompanied by significant increase in oil displacement efficiency. Michaels and Timmins studied the effects of transient contact angle alterations resulting from chromatographic transport of reverse wetting agents through unconsolidated sand. It was demonstrated that chromatographic transport of short-chain (C4 through C8) primary aliphatic amines can improve oil recovery and that the recovery increases with the quantity of amine injected (i.e., with either the amine concentration or the volume of the slug injected). Circumstantial evidence indicated that the increased displacement efficiency resulted primarily from transient changes in wettability of the porous medium.In the present investigation, additional information has been obtained on the effects of reverse wetting treatments and the mechanism by which increased oil recovery is accomplished.
SPEJ
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Mechanism of active silica nanofluids based on interface-regulated effect during spontaneous imbibition