Rock Physics
Links Between Seismic and Geologic Processes
Mavko, Gary1 (1)
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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California