Novel Approaches for Remaining Hydrocarbon Saturation Evaluation Through Interpretation of Multi-Detector Pulsed Neutron Logs

Abstract

Novel interpretation approaches for remaining hydrocarbon saturation evaluation were developed from our study and presented in this paper. Innovative power law relationships and algorithms are used for evaluating oil saturation from Carbon/Oxygen (C/O) logs and gas saturation from capture-to-inelastic count rate ratios, based on the principle of the modern multi-detector pulsed neutron tool responses and the total porosity rock model. C/O log interpretation parameters are determined from the crossplot of near detector against far detector C/O logs, and gas saturation interpretation parameters are obtained from the crossplot of near detector versus far detector capture-to-inelastic count rate ratios. An alternative fixed response line method is proposed based on a simplified C/O log response rock model. Integrated interpretation is applied through the post processing combining the interpretations of C/O logs and capture-to-inelastic count rate ratios, to derive the final result. The developed approaches have been applied to wells from Nigeria Delta and North Sea. Example results have successfully demonstrated greater advantages over the traditional methodologies. These new approaches have markedly reduced the saturation uncertainty related to wellbore effects, especially for wells with complex well completions and borehole fluid phase change. These results were subsequently useful information for the dynamic reservoir simulation models.