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ABSTRACT: Reservoir geochemistry of Geleki Field in Upper Assam Basin, India

Goswami, B. G., R. S. Bisht, K. L. Pangtey, J. H. Ganjoo, Rajiv Sharma, A. K. Sharma, N. J. Thomas, K. N. Misra, Kuldeep Chandra , Oil & Natural Gas Corporation Ltd, Dehradun, India

Reservoir geochemistry is increasingly being used in petroleum industry to find solutions to various production and reservoir related problems. Gas chromatographic fingerprinting, one of the most reliable tools to evaluate reservoir continuity, is used here to evaluate the continuity of three prominent Tipam sandstone (TS) reservoir units, TS-2, TS-3A and TS-5A1 of Geleki field in Upper Assam Basin of India. Gross compositional, gas chromatographic, stable carbon isotopic and GC-MS studies suggest that the organic matter is derived from the same source organics. Thermal maturity is also similar. Polar plots based on naphthenic peak ratios indicate that there is only limited lateral continuity in TS-2 and TS-3A reservoirs in the studied fault blocks. In TS-5A1 reservoirs, there is good lateral continuity within some of the blocks. However, no correlation was found among wells across the different blocks. No vertical/vertico-lateral continuity was found between TS-2 and TS-3A reservoirs in the studied wells. No gravitational segregation of reservoir fluids was found in these thick sands. These results indicate that these reservoirs are most likely compartmentalised, possibly due to the presence of shale bands or other permeability barriers and each compartment may be acting as a separate production unit. Therefore, there may be a need to review the pay-zone correlation and also to re-classify the thick TS-2 and TS-3A sands and subdivide them further into sub-units. Such an effort may help in designing the future exploration and development strategies of these sands.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia