Scale in Rock Physics - Caveats and a Remedy

Inversion of the seismic amplitude into impedance is attractive because impedance is a layer property while amplitude is a property of the interface between layers. Impedance is directly measured during controlled experiments in the lab and in the well, together with porosity, mineralogy, pressure, and saturation. As a result, one can first establish rock physics transforms from the rock’s elastic properties into its bulk properties and conditions and then apply them to the seismic impedance to describe the subsurface. The scale of data acquisition is very important in this workflow. Remember that while a rock physics transform, such as that between velocity and porosity, is established at the lab or log scale of only inches and feet, we aspire to apply it to seismic data on the scale of tens and hundreds of feet. Direct and unconditional use of such rock physics transforms, applied to seismic impedance volumes without accounting for scale effects, will produce erroneous results. We show that a new type of seismic attributes - cumulative attributes - can help remedy this problem.