A rock physics model-based approach to delineate deep and tight sand reservoir heterogeneity in the Bohai Bay Basin, China

Delineating sweet spots is critical for the exploration and production of oil and gas in deep and tight sand reservoirs. The lack of advanced and reliable methods makes this a challenge for geologists and geophysicists. This study introduces, for the first time, an integrated workflow that combines pre-stack seismic inversion with rock physics modeling to predict reservoir porosity and shale volume (V-shale) for sweet spot identification in tight sand reservoirs. A new elastic parameter, the density calculation index (DCI), is introduced which links acoustic and shear impedance for seismic density inversion, thereby addressing the long-standing problem of poor density inversion accuracy. A novel combined Sun–Walsh rock physics model, developed as part of this study, significantly improves V-shale evaluation from seismic data. The proposed three-step seismic inversion approach includes: (1) deriving acoustic and shear impedance from angle-stack seismic data using model-based inversion; (2) calculating density using shear impedance constrained by DCI, followed by porosity estimation from the density–porosity relation; and (3) evaluating V-shale using the α-parameter derived from the Sun–Walsh model and pre-stack inversion results. This integrated workflow provides an effective tool for building accurate 3D reservoir models, and is especially applicable to deep, low-porosity, tight sand reservoirs worldwide. • A new elastic parameter for seismic density inversion. • The Sun-Walsh model derived to improve the accuracy of V-shale seismic estimation. • Potential applicatoion to deep, low-porosity, tight sand reservoirs worldwide.