Determination of Residual Oil Saturation After Waterflooding

Abstract

Abstract This paper illustrates the use of several independent testing and calculational procedures for determining residual hydrocarbon saturations remaining in a reservoir after waterflooding. These methods consist of material balance calculations, analysis of well test data, pressure transient testing, core analyses, and pressure transient testing, core analyses, and borehole log calculations. Results of this work indicate: Good agreement was obtained between the several independent methods. Pressure transient testing is a valuable tool for measuring in-situ formation properties such as effective permeability to water and total compressibility. Values of compressibility obtained indicate gas saturation remaining after waterflooding is essentially zero. Water-oil relative permeability data is an important part of the analysis technique. Laboratory derived data should be carefully examined for validity. Field cases show that waterflood performance tends to verify laboratory kw/ko data as well as indicate residual oil saturation. Careful analysis of borehole logs can be very helpful. One of the field cases verifies the existence of saturation gradients, A comprehensive approach, utilizing all available tools, provided satisfactory and meaningful results provided satisfactory and meaningful results in both field cases reported. Introduction Depletion of domestic oil reserves in the face of increasing demands for energy has spurred development of new or improved techniques by which additional oil may be recovered from known reservoirs. Many of these reservoirs have already been depleted by waterflooding or by other secondary recovery methods. Whether tertiary recovery attempts are justified depends largely on a careful evaluation of the residual oil remaining in the reservoir. Most of the oil which is potentially recoverable by tertiary recovery processes is found in old fields where data are either scarce or are of poor quality. Types of data generally available are as follows: 1. Oil production history, usually on lease or farm basis. 2. Produced water-oil ratio and gas-oil ratio histories.