Seismic Reflections of Rock Properties

Dvorkin, Jack Petrovich¹ (1) Stanford University and Rock Solid Images, Stanford, CA

Seismic reflections depend on the contrast of the P- and S-wave velocity and density in the subsurface while the velocity and density, in turn, depend on lithology, porosity, pore fluid and pressure. These two links, one between rock's structure and its elasticity and the other between the elasticity and signal propagation, form the physical basis of seismic interpretation for rock properties and conditions. One approach to interpreting seismic data for the physical state of rock is forward modeling. Lithology, porosity, and fluid in the rock, as well as the reservoir geometry, are perturbed, the corresponding elastic properties are calculated, and then synthetic seismic traces are generated. The underlying supposition is that if the seismic response is similar, the properties and conditions in the subsurface that give rise to this response are similar as well. Systematically conducted perturbational forward modeling helps create a catalogue of seismic signatures of lithology, porosity, and fluid away from well control and, by so doing, sets realistic expectations for hydrocarbon detection and optimizes the selection of seismic attributes in an anticipated depositional setting. We show an example of such interpretation workflow and result at an offshore location.