Relationship between Velocity, Oil Saturation, and Flooding Efficiency

Abstract

Abstract Based on laboratory tests conducted with the use of fresh core samples aswell as a considerable amount of field data obtained from numerous water floodsin northeastern Oklahoma, it appears that for any given oil saturation there isa critical maximum velocity above which the oil-recovery efficiency falls offvery rapidly. In effect, when a water flood is operated above this criticalvelocity, the injected water-oil ratio rises extremely fast, thus shorteningthe economic life of the flood and reducing the ultimate oil recovery. Thiscritical velocity apparently varies considerably with the percentage of oilsaturation of the sand, so that in effect the higher the oil saturation at thebeginning of a flood the higher the velocity that can be used successfully. Inreviewing several of the earlier floods in the Mid-Continent area, it isconcluded that most of the failures were due to two things:too Iowan oilsaturation, such as 30 per cent, andtoo high water-injection rates. Although considerably more field data are necessary to establish definitelimits, it would seem that the proper field injection rate for a 330 by 330 or440 by 440-ft. spacing varies from approximately 1 bbl. per foot of sand perday where the oil saturation is as low as 30 per cent up to 5 bbl per foot ofsand per day when the oil saturation is as high as 45 to 50 per cent. Introduction With secondary recovery by water-flooding receiving more and more attentionthroughout the industry, a greater working knowledge of multiphase flow underfield conditions becomes more and more necessary. A great deal of research hasbeen carried on in highly idealized laboratory conditions, from which certaintrends have been indicated, but with few exceptions no direct application tofield use has been reported. Widely varying conclusions have been drawn fromthe mass of idealized laboratory experiments and often this divergenceapparently was due to the neglect of connate or interstitial water. Since interstitial water is such an important factor in water-floodingoperations, it then follows that any laboratory flooding experiment mustnecessarily take it into account; and since it is difficult to set uplaboratory models to allow for interstitial water, the next best procedure isto use fresh core samples for such tests. Even this procedure has itsdifficulties, inasmuch as it is possible to run only one flooding test on eachsample, as each sample differs somewhat in character from all other samples.However, this disadvantage can be overcome to a large degree by the use of anextremely large number of samples. T.P. 1592