In Situ Measurement of Residual Oil Saturation

The accurate determination of residual oil saturation is of critical importance in evaluating the feasibility of applying an enhanced recovery process in a specific reservoir. The economics of the new improved recovery processes are extremely sensitive to the residual oil saturation in place at the beginning of the project and to the conformance expected to be achieved within the project area. This means that both the amount and the distribution of oil remaining in place must be determined to adequately evaluate the potential of the venture. The only accurate means of determining the residual oil saturation is to measure it in situ within the reservoir zone of interest. In recent years, several methods have been developed to provide this measurement, including analyses of cores cut with a pressure core barrel, various advanced logging techniques, and the single-well tracer test. Each method has certain advantages and limitations, but field experience has shown that some methods are clearly superior to others. However, for some reservoir situations, one method may not provide all the information required to completely define the distribution and amount of remaining oil. These cases might require the application of two or more methods combined with an analysis of all available reservoir data. This paper will briefly summarize several procedures for determining residual oil saturation and. as pertinent, outline the advantages and limitations of each technique. The single-well tracer method will be described in more detail in terms of two recent field applications.