Elastic depth trends for siliciclastic sequences

Abstract

Elastic depth trends are an integral component of reservoir characterization whether explicitly or implicitly constructed. Applications to seismic data include migration velocity model building, pore-pressure prediction, inversion, and amplitude-variation-with-offset (AVO) analysis. In practice, workflows often involve fitting well logs with smooth curves, without reference to known lithology-dependent templates that could provide realistic constraints. We have constructed porosity-depth trends for shales and sandstones with reference to reliable measurements that span mechanical compaction and chemical diagenesis domains. These porosity trends are then used as inputs to well-established rock-physics models to estimate the median and bounding trends for acoustic and shear impedance. The resulting modeling has shown an important sensitivity to the pore-pressure regime (notably in shales) and the onset of cementation (in sands), among other variables. AVO predictions made from these trends provide a useful reference frame for anomaly prediction with depth, which is critical in frontier exploration.