Petrophysical analysis for evaluating the PY-3 reservoir has been carried out a number of times at different stages of field development. The PY-3 field is located in the offshore Cauvery basin, East Coast of India. The field was discovered in 1988 and put on production from 4 wells in the year 1997. The reservoir performance over the years has indicated a higher reserve base than volumetric estimates. The main reservoir sands belong to Nannilam Formation of Upper Cretaceous and are interpreted to be deposited as debris flows in a submarine slope setting from Sedimentological studies on conventional cores. The initial petrophysical studies assumed comparatively cleaner sands and used the basic Indonesian equations for water saturation estimations. In view of the higher reserve base indicated through reservoir performance, the petrophysics was re-studied. The first step was the revision of Rw based on produced water. Next, prior to carrying out the new log analysis, cores from different wells were examined for determining the Archie parameters. Based on the core-derived a, m, n and additional evidence of the shaly nature of this reservoir as observed from drilling of new lateral wells, the water saturation model was changed. Modified shaly sand equations were applied. The new analysis combined with re-mapping showed volumetric estimates matching with material balance. Consequently further field development plans have been envisaged. This demonstrates the need for an integrated approach for meaningful petrophysical analysis.

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