Laboratory Measurements of Relative Permeability

This paper presents the results of laboratory measurements of relativepermeabilities to oil and gas on small core samples of reservoir rock by fivemethods, and describes the influences of such factors as boundary effect, hysteresis, and rate upon these measurements. The five methods used were the"Penn State," the "single core dynamic," the "gasdrive," the "stationary liquid," and the "Hassler"techniques. In those methods in which the results are subject to error because of theboundary effect, the error may be minimized by the use of high rates of flow.In order to avoid complexities introduced by hysteresis, it is necessary toapproach each saturation unidirectionally. Observed deviations of relativepermeabilities with rate can be explained as a manifestation of the boundaryeffect, and disappear as the boundary effect vanishes. The results indicate that all five methods yield essentially the samerelative permeabilities to gas. Of the four methods applicable to thedetermination of relative permeability to oil, three, the Penn State, singlecore dynamic, and gas drive, gave relative permeabilities to oil which were inclose agreement. The Hassler method gave relative permeabilities to oil whichwere consistently lower than the results obtained by the other methods. Introduction The relationship between the effective permeability of a reservoir rock toeach of the fluids flowing through it and the corresponding fluid saturation isan important characteristic of the reservoir rock. Knowledge of thischaracteristic is and gas reservoirs and of the ultimate recovery to beexpected extremely important in the prediction of the behavior of oil undervarious operating conditions. These effective permeabilities are usuallyexpressed as the "relative permeability" to a fluid phase, defined asthe ratio of the effective permeability to the permeability of the rock to asingle phase at 100 per cent saturation. Relative permeability-saturation relations are not the same for all kinds ofreservoir rock, but may vary from formation to formation, and within thedifferent portions of a heterogeneous formation. In studying the performance ofa specific reservoir, it is necessary, then, that the relative permeabilitycharacteristics of the individual portions of the reservoir be measured. Thesemeasurements may be made in the laboratory on small core samples from thereservoir. Various techniques have been proposed for the measurement in the laboratoryof relative permeability-saturation relations. In varying degree, difficultiesattend the use of all of the methods which have been proposed. It is thepurpose of this paper to discuss the factors which influence the measurement ofrelative permeability, the difficulties encountered in several methods, and topresent comparative results obtained by the use of various techniques. T.P. 3020