Beyond Conventional Logs: Redefining Geosteering in Carbonate Reservoirs Using Integrated LWD Measurements While Drilling

Abstract

Geosteering horizontal wells in complex, heterogeneous carbonate reservoirs presents a significant challenge, as lateral variations in permeability are often not captured by conventional logging measurements. This paper details a novel workflow that leverages advanced Logging-While-Drilling (LWD) diagnostics to identify and steer within the best carbonate rock quality for enhanced productivity or injectivity. This is achieved through robust real-time radioactive-source-free porosity and permeability indicators derived from LWD advanced measurements such as Nuclear Magnetic Resonance (NMR) and LWD Sonic and validated by independent formation testing while drilling (FTWD) measurements leading to optimized well placement beyond traditional structural positioning. The advanced methodologies were developed from multiple wells analyses where NMR and sonic porosity and permeability curves have enabled real-time well placement strategy as well as advanced post well interpretations. Deeper look into NMR data also showed how the NMR T1 distributions processed with default bound fluid cutoffs, failed to differentiate between permeable and impermeable zones. Advanced processing of NMR T1 distribution data revealed clear rock quality differences, prompting a reprocessing of the logs with a modified T1 cutoff to accurately reflect fluid mobility. Based on this enhanced analysis, a simplified "free fluid ratio" (FFR) curve was created as a direct, real-time geosteering indicator. Several horizontal wells were then steered using this FFR curve as the primary steering parameter, with azimuthally oriented Formation Testing While Drilling (FTWD) used for independent validation. Horizontal wells were successfully steered using the NMR-derived porosity and permeability curves keeping the wellbore in the zone with the highest rock quality. Mobility data calculated from FTWD pressure points in the lateral sections showed a strong correlation with the NMR-derived permeability, validating NMR-based FFR as a reliable permeability indicator. The conclusion is that this integrated approach enables effective navigation of complex reservoirs and maximizes contact with the most productive intervals, which would have been ambiguous using standard logs alone. This paper introduces powerful workflows derived from LWD NMR and sonic as novel real-time geosteering parameters in carbonate reservoirs. The primary innovation is the integrated workflow that combines advanced multiple LWD sensors analysis with FTWD data to de-risk well placement in reservoirs with significant lateral porosity and permeability variations. This methodology allows operators to shift from traditional structural steering to proactive petrophysical steering, ensuring horizontal well paths are optimized for fluid mobility and ultimate production potential.