The Accuracy of Pulsed Neutron Capture Logs for Residual Oil Saturation

Abstract

ABSTRACT Pulsed neutron capture (PNC) logs have been used to determine residual oil saturations for many years. A previous study found that at low values of residual oil saturation (ROS) conventional PNC logging techniques did not have the accuracy necessary for enhanced oil recovery decision making requirements. Special log-inject-log techniques were developed in order to reduce the uncertainty in values of ROS measured with PNC logs. A study of the uncertainty associated with ROS values determined with PNC logs was made using Monte Carlo simulation techniques. Field data was obtained from tests reported in the literature. Using a more realistic confidence interval of 95%, the expected accurace of the ROS values was found to decrease by at least a factor of two in all tests. Additional uncertainty introduced by the log-inject-log process was not modeled.