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Integrated Formation Evaluation Using Advanced Logs to Understand Reservoir Productivity

Abstract

Miocene clastic reservoirs of Mumbai offshore always pose immense challenges because of their highly varying reservoir property. Therefore, accurately determining petrophysical properties and geological uncertainties is of utmost importance. In this study advanced integrated petrophysical analysis were performed to get an insight about the formation and to analyze both the flow behavior and sand quality of the reservoir. Borehole micro-resistivity images provide the best resolution of the borehole wall. Elemental spectroscopy results were combined with the borehole micro-resistivity images to produce a core-like facies model for detailed documentation of the sedimentological history. Thin-section core analysis indicated that the sand varies from quartz arenite to lithic-wacke. Magnetic-resonance data helps understand the lithology-independent porosity. High-resolution image-derived results, and integrated core study helped characterize the reservoir sands, while well test data cross-validated the results derived from the other studies. Micro-resistivity images revealed that the sand and silty-sands comprised fluvial deposits formed by bars and channel fills. From the spectroscopic studies, the reservoir sands were characterized into four major facies: clean sand, sand, shaly-sand, and sandy-shale. Among them sand and sandy shale were found to be the producing facies. Integrated resistivity measurements were used to estimate a sorting index which indicated well sorted nature of sandy-silts as they settle out of suspension. Meanwhile sands show varying sorting across the profile. Magnetic-resonance data indicates fair amount of free fluid distribution in the sand units. Well testing results clearly reveal the potential of the probable reservoir sands to produce, as the sandy-shale and reservoir sand facies produced gas correspondingly at a rate of 1,77,209 m3/day and 2,38,667 m3/day respectively.