Improved Determination of Hydrocarbon Saturation in an Unconsolidated Heavy Oil Sand Undergoing Cyclic Steam Stimulation with an Advanced Slim Pulsed Neutron Logging Technology: A Case Study from Kuwait

Abstract

This paper presents a field application of an advanced slim Pulsed Neutron Logging tool (PNL) for improved determination of hydrocarbon saturation as a key basis to evaluate the reliability of an ongoing enhanced oil recovery (EOR) cyclic steam stimulation (CSS) process in an unconsolidated heavy oil sand in Kuwait. The new PNL tool was used to evaluate changes in oil saturation and to track steam movement as part of the ongoing EOR CSS project in the field. This improved determination of hydrocarbon saturation is performed as a baseline prior to CSS and then used for future time-lapse evaluation of effectiveness of recovery during and after CSS using both PNL sigma and inelastic/capture or carbon/oxygen measurements. Its features enhanced capture and inelastic spectroscopy performance, particularly at high temperatures in places where CSS is ongoing due to its 175°C rating compared to 150°C from legacy tools. Gas, Sigma and Hydrogen Index (GSH), Thermal Decay Porosity (TPHI), lithology, Inelastic Capture (IC) mode was ran at 200 feet per hour (fph); twice the speed legacy PNL tool. Its 3 passes provided better performance than the 5 passes of legacy tool deployed under the same conditions, illustrating its better measurement accuracy. Inelastic spectroscopy logs from near, far detectors provided data for fluid analysis, which demonstrated the benefits from its elevated specifications. Its spectral yields’ results showed better accuracy and improved repeatability between different passes under the same well conditions in spite of logging at twice the speed. Compared to legacy tool, the new PNL technology provided enhanced detectors, new pulsed neutron generator (PNG) and pulsing scheme designed to optimize the gas/steam, sigma and neutron porosity measurements in terms of accuracy. Its faster logging and less exposure time makes it a better fit. Its PNG source and detectors minimize the spectrum degradation caused by high temperatures, hence better signals. The hydrocarbon saturation from its Carbon/Oxygen ratio and Total Organic Carbon (TOC) derived methods demonstrated consistency and cross validation over the logged interval. The advanced PNL tool fits better compared to the legacy PNL with improved repeatability and excellent precision. It now provides the basis for a reliable determination of hydrocarbon saturation, which will improve the evaluation of EOR CSS ongoing project.