A Proactive Geosteering Approach Integrating Advanced LWD Nuclear Magnetic Resonance and Deep Azimuthal Resistivity Tools for Landing a Deep Jurassic Horizontal Well in the Best Carbonate Reservoir Facies

Abstract

The Jurassic Marrat formation in West Kuwait is a tight and heterogeneous carbonate reservoir in which petrophysical characteristics lead to a limitation in the predictability of reservoir properties. Landing a later well exposes operational risks, therefore LWD triple combo is excluded to avoid environmental issues and cost effects. Instead, LWD-NMR combined with Deep Azimuthal Resistivity tools emerges as the optimum solution to evaluate the formation and optimize well placement in the best reservoir quality. NMR is utilized for accurate porosity because it is independent of lithology. The T2 distribution is a direct indicator of porosity and permeability. DAR is an azimuthal propagation resistivity tool that can greatly reduce the risk of misplacing the wellbore while drillingextended reach and complex 3D horizontal wells. Marrat reservoir tends to have high resistivity, but theporosity isn't always ideal. It makes geosteering operation more challenging if only gamma & resistivity logs are used to overcome this challenge, LWD-NMR in combination with DAR maximizes the reservoircontact and produces from the best reservoir quality. Deep Azimuthal Resistivity shows the F-11 surface was found 25 ft. shallower than the A-1 plan. The plan was modified in real-time to ensure a successful landing within the target zone, the starting plan of 3.8 DLS was modified and increased to 4.65 DLS to account for the shallower F-11 with the aim of achieving a TVD depth of 20 ft. inside the reservoir zone. After landing the well at 90 deg inclination following the NMR & DAR signatures, we continue building the inclination angle to 90.5 deg to gently upwards cut stratigraphically across the section and to penetrate the optimum reservoir zone before leveling off gradually to 89.3 deg following NMR & DAR signature to maintain the well in the best reservoir facies. During the geosteering operation in the F-11 zone, a decrease in porosity from 16 pu to 2 pu was detected by the NMR. Consequently, a real-time adjustment was made to avoid the tight area and guide the well toward the sweet spot in the F-11 zone. The combination of NMR and DAR tools successfully landing of the well in the F-11 zone with high-confident hydrocarbon potential.