This procedure, in which the wettability change is assumed to be the important enhanced recovery mechanism, is recommended for determining the applicability alkaline waterflooding in specific light-oil reservoir systems. Introduction The wettability of petroleum reservoir rock, its estimation in laboratory tests, and its effect on the displacement of oil by water have been the subject of a considerable and growing body of literature. Craig presented an excellent review of developments in this presented an excellent review of developments in this field so another discussion will not be given here. Recent investigators generally agree that preferred wettability is not a discrete-valued function, oil-wet or water-wet, but can span a continuum between these extremes. It has been demonstrated with artificial wettability systems using low-viscosity oils that waterflooding to a given water-oil ratio (WOR) becomes increasingly more efficient as a sand becomes more water-wet. It is not altogether certain, however, that waterflooding under strongly water-wet conditions is always most efficient in real reservoir systems. An example of this is given by Salathiel, who found lower residual oil saturations in mixed wettability systems than would occur under strongly water-wet conditions. This effect was attributed to gravity drainage across bedding planes. Most recently, Treiber el al. noted that a large number of reservoirs are more oil-wet than water-wet.It has generally been found, however, that causing a reservoir to become more water-wet by chemical means during the course of a waterflood results in an increase in oil recovery over that of an unaltered displacement by water alone. This has been demonstrated by Wagner and Leach, and by Leach et al. using a refined oil containing an amine to simulate an oil-wet system and an aqueous acid solution to reverse wettability. Mungan and Emery et al. obtained the same result using a sodium hydroxide (NaOH) solution to alter the wettability of a crude oil-brine-sand system. Alkaline waterflooding has been found under certain circumstances to increase oil production by low interfacial tension displacement and by rigid film breaking as well as by favorable wettability alteration.Two types of screening procedures for recovery estimation have been reported, both of which attempt to duplicate reservoir wettability by contacting oil, water, and mineral for long periods of time. A contact-angle measurement technique was described for wettability and wettability alteration estimation and for wettability estimation alone. The measurement is made after water displaces oil from a plane mineral surface in contact with the oil for various times. To obtain no further changes, the aging times required varied from 200 to 2,400 hours for different reservoir systems. The amount of additional oil obtainable by an alkaline waterflood is inferred from the difference between the normal water-oil-solid and alkaline water-oil-solid contact angles. This type of test can only estimate wettability-change increased production. production. JPT P. 1335

A method was developed to collect interface-active film material from theoil/water interface. The film-forming material was subjected to infrared andmass spectrometric analysis. The combined analysis data indicate that the polarorganic material consists to a large extent of aliphatic esters of aromaticacids. The existence of smaller amounts of ketones, aldehydes, naphthalene andanthrazene derivatives, carboxylic acids and organic nitro compounds was alsoindicated. Long chain aliphatic material was found incorporated within themultilayered film structures. The molecular weight range of the inter faciallyadsorbed organic molecules lies between 200 and 420, with the accent on thehigher mass values. The surface exposed groups of the multilayer films arethought to consist of a closely packed array of CH, groups. A hypothesisconcerning an interrelationship between the formation of interfacial films andparaffin deposition is given. INTRODUCTION THE EXISTENCE OF FILMFORMING COMPOUNDS in crude oils and the possibleimplication to some problems of concern to the petroleum industry has beenrecognized for a number of years. It has been found that the surface exposedgroups of polar-non-polar molecules, adsorbed on a solid or a liquid surface, will completely determine the subsequent wettability characteristics of thelatter (1). The relevancy of this fact to problems such as relativepermeability measurements, secondary recovery methods and paraffin depositionhas been mentioned by several researchers (2, 3, 4). Attempts have been made inthe past to isolate film forming compounds from crude oils and to define theirchemical nature. Metalporphyrins complexes (5, 6), free naphthenic acids, acidanions and their salts (7), and highly oxygenated low molecular weightfractions of the resin and asphalt fractions of crude oils (2) have been listedas interface-active compounds. A severe crystal growth modification in waxslovent mixtures, induced by asphaltic material, has been reported by Birdwell(8), Chichakli (9) and others (10). Patton (11) found, during paraffindeposition studies, that the presence of a high boiling point crude oilfraction, both in the wax solvent system and as a pre-adsorbed film, inhibitedthe formation of paraffin deposits. A film balance study of the physicalcharacteristics of films formed by benzene solutions of crude oils, includingtheir distillation and chromatographic fractions at the oil/water interface, was described earlier (12, 13). The indication was that the 700°F+ distillationresidual and, in turn, their asphaltic sub fractions are the major contributorsof interface-active material to the films formed by the original crude oils.Hence, without trying to adopt any specific model for the structure of acolloidal " asphaltene particle," it seemed that either the asphaltic fractionscontained free polar molecules a priori or the benzene as a solvent played arole in " activating" polar molecules through destruction of a number ofasphaltene particles.

No abstract

on a flurry of activities that range all the way from fault-finding exercises to true efforts Coal, oil shale and tar sands are reviewed of finding solutions to the problem. In view in an effort to delineate the applicability of of the projected ever-widening gap between in-situ exploitation meihods and their potential energy demand and supply, the concept of energy impact on the domestic energy situation in the sources competing on the basis of economics is years to come. In-situ exploitation is favored being re~laced more and more by the concept of because of some inherent environmental advantages complementary energy sources. Under the latter over mininglsurface conversion methods; because., concept, economics, rather than playing the tiithproper emphasis, the processes could consinglemost important role, shares the limelight ceivably be commercialized in the early 80's; with environmental considerations and the proband finally because present oil and gas probabilityof technological success within a duction technology, specifically from the area desired time-frame. of tertiary oil recovery, f.sthought to be applicable to a large degree. Values for domestic Since the "energy crisis" has been adopted, in-situ recoverable resources are developed for not only by industry and government but also several processes by (1) excluding non-applicable by the news media and the public-at-large, a resources and (2) applying a compound r@covery host 05 energy-related articles has made its efficiency to the remainder. The amount and the appearance in every conceivable journal and character of end products, achievable by each magazine. Often, in the more popular magazines, process, are derived. Product end use is sugenergy sources such as increased imports, coal gested and estimated product values are developed . gasification and liquefaction, surface con-While a considerable research and development version

on a flurry of activities that range all the way from fault-finding exercises to true efforts Coal, oil shale and tar sands are reviewed of finding solutions to the problem. In view in an effort to delineate the applicability of of the projected ever-widening gap between in-situ exploitation meihods and their potential energy demand and supply, the concept of energy impact on the domestic energy situation in the sources competing on the basis of economics is years to come. In-situ exploitation is favored being re~laced more and more by the concept of because of some inherent environmental advantages complementary energy sources. Under the latter over mininglsurface conversion methods; because., concept, economics, rather than playing the tiithproper emphasis, the processes could consinglemost important role, shares the limelight ceivably be commercialized in the early 80's; with environmental considerations and the proband finally because present oil and gas probabilityof technological success within a duction technology, specifically from the area desired time-frame. of tertiary oil recovery, f.sthought to be applicable to a large degree. Values for domestic Since the "energy crisis" has been adopted, in-situ recoverable resources are developed for not only by industry and government but also several processes by (1) excluding non-applicable by the news media and the public-at-large, a resources and (2) applying a compound r@covery host 05 energy-related articles has made its efficiency to the remainder. The amount and the appearance in every conceivable journal and character of end products, achievable by each magazine. Often, in the more popular magazines, process, are derived. Product end use is sugenergy sources such as increased imports, coal gested and estimated product values are developed . gasification and liquefaction, surface con-While a considerable research and development version