Abstract

The Barail formation of Upper Assam Basin was deposited in fluvio-deltaic depositional environment where sand acts as potential hydrocarbon reservoir and Barail coal-shale unit act as a cap rock. Generally, it has been observed that, in case of an unconsolidated and undercompacted sand the acoustic impedance contrasts between brine sand and shale are very less. However, when the reservoir sand is saturated with hydrocarbon specially gas, a prominent impedance contrast has been observed in the sand-shale interface. The above situations are constrained by boundary conditions of fluid saturation, reservoir thickness and depth.