Three-Phase Saturation Evaluation Utilizing Multidetector Pulsed Neutron Logging in Freshwater Environments: A Guide for Sidetrack Drilling Optimization

Abstract Sidetracking a well involves drilling a secondary wellbore that branches off from the original wellbore. This technique is critical in hydrocarbon exploration because it bypasses the unproductive sections of an existing well and increases production potential from commercially viable reservoirs using a new wellbore. This paper focuses on multidetector pulsed neutron well logging applications for characterizing reservoir petrophysical properties to optimize the sidetrack drilling pathway and determine perforation placement. A slimhole multidetector pulsed neutron logging tool can be deployed through tubing to record inelastic and capture pulsed neutron datasets. In contrast to open-hole resistivity log-based saturation analysis, pulsed neutron well logging provides non-resistivity-based data for saturation analysis. The acquired data analysis allows us to evaluate the volumetrics of the cased formations and identify reservoir fluid contacts. With the ability to delineate the reservoir properties behind one or multiple casings, pulsed neutron well logging can be employed to optimize sidetrack drilling operations and enhance the precision of sidetrack wellbore trajectories. We demonstrate the application of pulsed neutron logging to a well in western Africa to evaluate multiphase formation saturation for optimized sidetrack drilling. The salinity of the formation water was less than 20,000 ppm NaCl equivalent. In this low-salinity water environment, salinity-independent carbon-oxygen (C/O) logging was performed to differentiate oil from water. An inelastic gas-sensitive gamma-ray ratio-based measurement, which can be used in freshwater environments, was also adopted in the saturation analysis workflow. The two inelastic measurements were combined simultaneously to quantify the formation volumes of the three fluid components. The saturation analysis results revealed a three-phase saturation profile as well as water-oil and oil-gas contacts. The multidetector pulsed neutron data-based saturation results enabled us to understand the current reservoir fluid distribution, differentiate between productive and unproductive formations, and optimize the sidetrack drilling pathway. This eventually contributed to improved reservoir production management.