Rock physics modeling and quantitative seismic interpretation workflow for organic-rich mudrocks

Abstract

A quantitative seismic interpretation workflow based on rock physics was developed for an organic-rich mudrock formation in order to estimate porosity, and organic matter and clay contents from seismically-derived acoustic and shear impedances. This deterministic workflow consists of: developing a rock physics model that accurately estimates the elastic properties of the formation; finding inter-relationships between the formation's petrophysical properties; and validating the model after upscaling and applying it to seismically-derived acoustic and shear impedances. By analyzing wireline data from this organic-rich mudrock formation, we find that the P-wave velocity at fixed porosity may vary by as much as 1.0 km/s, while the respective variation in the S-wave velocity reaches 0.5 km/s. A robust discriminator for velocity appears to be, in addition to the total porosity, the volumetric fraction of the soft components of the solid matrix where the kerogen is included, namely the sum of the clay and kerogen. The ensuing velocity-porosity-mineralogy relations are accurately described by the soft-sand rock physics model. Thus, an attempt to interpret seismically-derived impedance volumes based on rock physics modeling is performed after simplifying the rock's petrophysical variables by building site-specific internal relations between mineral's volume fractions that comprise the rock's solid matrix. This workflow helps in hydrocarbon exploration by identifying favorable areas with relatively high porosities and organic matter content.