Reservoir characterization for hydrocarbon detection using Amplitude Variation with Angles constrained by localized rock physics template

Seismic data are prone to ambiguities because different scenarios of geological structures and rock properties can produce similar seismic reflections. The poorly compacted sandstone reservoirs of the 'Jay' Field produced seismic amplitude anomalies which may not be diagnostic of hydrocarbon presence. In this study, the different seismic amplitude reflections from 'Jay' Field reservoirs were investigated to determine the effect of fluids and lithologies on the observed seismic amplitudes for possible hydrocarbon identification away from well location. Amplitude Variation with Angles (AVA) and Rock physics techniques were used to analyze amplitude responses from sandstone reservoirs. These seismic amplitudes were extracted from the near and far partial angle stacks to identify changes in amplitudes with angles. Reservoir properties were examined to determine their influence on seismic responses through Rock Property Template (RPT) analysis. Well logs revealed that three of the seven identified reservoirs (Sands A, B and C) are brine saturated, Sand D is oil while Sands E, F and G are gas bearing. The reservoirs stratification is mainly the juxtaposition of low impedance sandstone and high impedance shale, such that P-velocity and density significantly influence impedance contrast in sandstone reservoirs and shale lithologies respectively. Changes in seismic amplitudes from near to far angles around Well location show that the gas reservoirs produce different AVOs that correspond to Classes II, III and IV respectively. The established Well log RPT supports AVA results of gas presence in the identified area away from Well location. This helps to reduce the risk associated with seismic amplitude ambiguities and enhanced certainty of gas presence at the location away from Well log information. In similar geological scenario, this work can serve as a useful guide to gas sand detection from seismic data.