Sandstone discrimination in the Faja Petrolífera del Orinoco, Venezuela: Lithology delineation using 3D-3C seismic data

Abstract

The Faja Petrolífera del Orinoco (FPO) in Venezuela is the most extensive accumulation of heavy oil in the world. Consequently, the main objective is to use 3D-3C multicomponent seismic data for sandstone discrimination in the Petrocedeño block in the FPO, with the aim of providing information that contributes to better characterization of heavy-oil deposits. Log- and seismic-frequency-scale rock-physics analysis for lithology discrimination was performed, revealing that sandstones and shales might be discriminated using acoustic-impedance (AI) and VP/VS attributes. Shales have lower acoustic impedances and higher VP/VS than sandstones. Therefore, a cutoff of 2.45 in VP/VS ratio was set to separate sandstones and shales. A model-based acoustic seismic inversion was performed, and VP/VS ratio volume was estimated, interpreting horizons in PP and PS volumes, then shrinking PS to PP reflection time. Consequently, lithology distribution could be mapped using those volumes. Geologically speaking, the lower interval with more sandstone corresponds to a fluvial environment, whereas the upper interval is deltaic with more proportion of shale, according to regional geology as well.