The Use of Well Logs To Monitor a Surfactant Flood Pilot Test

Abstract

A logging program has been developed and used successfully to monitor the performance of a surfactant flood pilot test in Loudon field, Fayette County, IL. This program consisted of induction and carbon/oxygen (C/O) log measurements that were made repeatedly in five observation wells, producing time-lapse records of oil saturation changes. To enable use of induction logs, the observation wells were completed with fiberglass casing. Special efforts were made to maximize the accuracy of the oil saturations calculated from logs. These efforts included use of pressure core measurements of residual oil saturation for calibrating log responses, laboratory measurements of the electrical properties of cores, and special wellsite calibration and quality control procedures. The log responses in each observation well provided essential data for evaluating pilot performance. The logs measured pre- and postflood oil saturations as well as the arrival time, oil saturation, and duration of the bank of mobilized oil. Vertical stratification effects also were observed. The combination of induction and C/O logs proved an effective means of monitoring a surfactant flood. Saturation measurements from the C/O log complemented the induction log results very well, providing better vertical resolution and a response independent of salinity and formation electrical properties.