Reservoir Characterization in Cased Hole: Evaluation a Pulsed Neutron Sigma Workflow for Hydrocarbon Saturation Analysis in the Absence of Open-Hole Logs

Abstract

Accurate characterization of reservoir properties such as lithology, porosity, and fluid saturation is foundational for effective resource evaluation and field development. While open hole logging is the industry standard for petrophysical analysis, operational complications like poor borehole conditions, often necessitate immediate casing, precluding open-hole data acquisition. This thesis describes a case study from Well ALG-1 TAGI (Trias Argileux Gréseux) reservoir, where severe borehole challenges resulted in the loss of primary open-hole logs and created substantial uncertainty regarding productive zones and fluid contacts. To address this, an advanced cased-hole workflow using Pulsed Neutron Sigma logging (RMT-I) was implemented. Deployed through 7-inch casing, the tool delivered high-quality pulsed neutron capture data, enabling direct calculation of hydrocarbon saturation. Robust interpretation identified three distinct hydrocarbon-bearing intervals, guided precise selection of perforation zones, and confirmed zonal isolation using oxygen activation. Post-perforation production testing validated the cased hole interpretation, yielding commercial oil rates and underpinning the well’s successful completion. This work demonstrates that modern cased-hole pulsed neutron logging is not only viable but can be transformative in challenging conditions where open-hole analysis is impossible or incomplete. The methodology presented enables the salvage of well value, delivers reliable reservoir insights, and optimizes economic outcomes without the need for risky or expensive intervention. These findings expand the application domain of cased-hole evaluation, offering a proven alternative for reservoir analysis and development planning in both new and legacy wells