Abstract

Commercial gaseous hydrocarbon has been established from multilayered reservoirs within the Bhuvanagiri Formation in the Ariyalur-Pondicherry subbasin, but sustained production is obtained from only a few wells of the Bhuvanagiri Field. This has necessitated developing an integrated depositional model dovetailing distribution of favorable reservoir areas of the Bhuvanagiri Formation within the subbasin. Root-mean-square amplitude attributes and spectral decomposition attributes, along with RGB blending of spectral slices at different frequencies, have revealed a conspicuously northeast-southwest-trending channel within the Bhuvanagiri Formation. From well, sedimentological, and biostratigraphic data analysis, a deepwater turbidity channel model for the Bhuvanagiri Formation has been postulated. Deciphering the facies distribution pattern vertically and laterally within the turbidity channel is often complex and challenging. Integrated analysis of available laboratory data, petrographic, and scanning electron microscopy studies indicate poor porosity and permeability because of clay coating on grains, occurrence of authigenic clay as pore fill, cementation, and other diagenetic changes that have made reservoir characterization increasingly challenging. Four major lithofacies assemblages have been identified: basal lags, slumps and debris flows, arenaceous coarse-grained stacked channels, and fine-grained channel levee with characteristic log and seismic responses. To characterize the lithofacies, various crossplots have been generated by using processed logs to derive interrelationships between reservoir facies and log impedance. A model-based inversion has been attempted, which resulted in fairly satisfactory output with likely discrimination of reservoir and nonreservoir in an unexplored area within the field. The outcome would facilitate further exploration and delineation activities within the Bhuvanagiri Formation in the Ariyalur-Pondicherry subbasin.

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