Single-Well Chemical Tracer Method to Measure Connate Water Saturation
Authors: Deans H.A. , Shallenberger L.K. 
Published: December 2007

This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., April 22–24, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
A previously-described single-well tracer test for measuring residual oil saturation in watered-out formations has been modified and extended to permit measurement of connate water saturation in formations producing water-free oil. The method provides a viable alternative to oil-base coring as a means for obtaining saturations for use in making reserve estimates or in calibrating saturation logs. The measured saturation represents an average value for a much larger reservoir volume than that sampled by logs or cores.
The connate water saturation test cons of three phases:injection of a bank of crude oil containing propyl formate, the primary tracer,reaction of part of the primary tracer,reaction of part of the propyl formate to form propyl alcohol, the propyl formate to form propyl alcohol, the secondary tracer, andproduction, sampling and analysis of the injected fluid to obtain concentration profiles for the two tracers.
Because of their different affinities for water, the two tracers separate as they move through the formation to the wellbore. The degree of separation is related to the amount of immobile water present in the formation — the greater the separation, the larger the connate water saturation.
The method has been field tested, and the results of the field test are in good agreement with log and core data.

Introduction
The use of a single-well tracer method to measure residual oil saturation in watered-out formations has been described by Tomich et al. The tracer method has now been modified and extended to permit in-situ determination of connate water saturation in a formation producing water-free oil. The same procedure can producing water-free oil. The same procedure can thus be used to measure the two saturations in a given formation that delimit the recovery attainable by waterflooding. The method also provides a viable alternative to oil-base provides a viable alternative to oil-base coring as a means for obtaining saturations for use in making reserve estimates or in calibrating saturation logs directly in the zone of interest.
In-situ chemical tracer tests avoid many of the limitations of core analysis and well logging, the most commonly used methods for determining fluid saturations.