Rock Physics Links Between Seismic and Geologic Processes

Mavko, Gary¹ (1) Stanford University, Stanford, CA

A powerful strategy for minimizing uncertainty in seismic interpretation is to develop means to quantify and incorporate geologic constraints into the Rock Physics models. We do this by modeling elastic properties, and hence, seismic amplitudes in terms of sedimentary parameters that control reservoir quality, and that also are consistent with the conventional geologic interpretation. Textural parameters that impact both reservoir quality and elastic (seismic) signatures include mineralogy, grain size, sorting, cement, and shaliness. Hence, these are the key parameters linking the depositional processes and their seismic signatures. In addition, post-depositional processes impact elastic signatures via compaction, pressure solution, dissolution and alteration, and cementation. Stratigraphic variations can often be described with sorting and shaliness models. When properly calibrated using well data, they provide the means for predicting the seismic signatures of depositional trends away from the well.

Particular modeling challenges come from fine-scale textural variations that are below well-log resolution. An example is mm-scale clay lamination, which can substantially increase Poisson's ratio, reduce fluid-substitution signatures, and introduce anisotropy. Another challenge of fine-scale structures is the role of clay within the rock matrix. Load-bearing vs. pore-filling clay requires different fluid substitution procedures, and may even have an impact on the effective stress response of velocities. Our challenges include refining rock models to incorporate the fine-scale textural variations, and learning how to infer subresolution texture from depositional models.