Abstract
To be of practical use for reservoir characterization, rock physics models are often perceived as too complicated and as dependent on too many difficult-to-measure parameters. Here we demonstrate how careful calibration of a common and quite simple rock physics model can provide valuable insights into the reservoir and seal elastic properties as function of porosity, fluid and mineral properties, andnet-to-gross. The model canbe used for quantitative seismic interpretation of reservoirs with variable net-to-gross and porosity away from well control.
We show that the Hashin Shtrikman Upper Bound is useful to model the compressional and shear velocities of grain-supported clean sandstones as function of porosity, whereas matrix-supported claystone compressional velocities follow the concaveHashin Shtrikman Lower Bound. The corresponding shear velocity shale data plot similarly but for the Lower Bound to be useful to model shale shear velocities the clay-bound-water needs to be modeled with a small but finite shear stiffness. This update alsoimproves the shale compressional velocity model fit. The resulting unified compressional and shear Hashin Shtrikman model allows for the calibration of a sand-shale mixing model that can be used to interpret seismic-derived acoustic and shear impedances in terms of sand net-to-gross and porosity away from well control.
