ABSTRACT

The paper presents a review of the results of some petrophysical studies conducted on core samples from productive horizons of Lakwa, Galeki and Rudrasagar oil fields in the Upper Assam Valley in northeastern India. In all the cases, although the limiting formation factor - porosity relations are found to closely agree with the Humble's equation, the saturation exponents corresponding to the generally fresh formation waters have been found to be substantially lower than the widely accepted value of 2. The measurement of saturation exponent at different saturant salinities confirms the applicability of Waxman and Smits' equation to the given reservoirs. Furthermore, the wide divergence observed between apparent formation factor and limiting: formation factor necessitates large corrections to the resistivity-derived apparent formation factor before its conversion into porosity. The comparison of the relations between limiting formation factor and porosity as well as between resistivity index and water saturation among the three fields indicates that the Barail reservoirs of Kudrasagar field, when compared to the Tipam reservoirs of Lakma and Galeki fields, apparently provide easier path for electrical current flow, in spite of the expectedly higher tortuosity and larger variations in the cross-sectional area of the pore channels. This may be due to the relative abundance of pyrite in the Barail reservoirs or due to the limitation of the experimental results on account of the absence of simulated insitu overburden pressure conditions during the experiments or both. The review has brought out the necessity of continuing such experimental work, particularly under simulated insitu conditions, on cores from other fields in India.

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