Pre-Stack Seismic Inversion and Amplitude Versus Angle Modeling Reduces the Risk in Hydrocarbon Prospect Evaluation

Abstract

Pre-Stack seismic inversion and Amplitude versus Angle (AVA) techniques were used in for direct hydrocarbon identification (DHI) and to understand better the risk during hydrocarbon prospecting. In order to understand and predict the seismic response for different fluid type and lithologies pre-stack seismic inversion and AVA modeling based on existing well logs information were performed. An optimized seismic inversion workflow that includes conditioning of seismic data followed by seismic petrophysics and rock physics modeling in combination with fluid substituted logs was used to predict the seismic response for different fluid types. Inverted rock properties of a wedge model were then correlated with seismic response for DHI. Another hydrocarbon prospect was studied based on AVA modeling response. AVA effects on angle gathers provide basic information on the lithology and pore fill contents of the rocks under investigation. To perform the AVA modeling, a series of forward models in association with rock physics-modeled fluid-substituted logs have been developed and associated seismic responses for different pore fluids and rock types studied. The results reveal that synthetic seismic responses together with the AVA analysis show changes for different lithologies. AVA attributes analysis show trends in generated synthetic seismic responses for different fluid-substituted and porosity logs. Reservoir modeling and fluid substitution increases understanding of the observed seismic response. It ultimately leads to a better reservoir prediction with delineation of sweet spots and improved volumetric prognosis. Assessing the effect of fluid-substituted logs for different lithologies and associated AVA seismic response can improve the prediction in reservoir characterization. Truly integrated studies of seismic, geology and well data will reduce the drilling and development risks even further.
Key Words: Pre-stack seismic inversion; Wedge model; Amplitude versus angle (AVA); Fluid substitution; Intercept (I); Gradient (G); Rock physics; Derisking and forward modeling