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From
Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Calgary, Alberta, Canada, June 19–22, 2005 Seismic Sensitivity of Vuggy Porosity: Example
from Abstract: One of the important issues in the characterization
and modeling of carbonate reservoir strata that remains to be effectively
addressed is the seismic characterization of touching-vug pore systems
and the integration of seismic information into fluid-flow models. The
lower San Andres carbonate sequence exposed in the Lawyer Canyon outcrop,
New Mexico, provides an excellent example of ramp-crest grainstones having
both interparticle porosity and touching-vug porosity. Using an outcrop-based
3-D lithofacies/porosity geocellular model, we calculated velocity from
porosity using a linear relationship and generated 3-D synthetic seismic
models to study seismic responses to vuggy porosity. Under the assumption
that the seismic P-wave misses all the vuggy porosity and seismic detects
vuggy porosity only by responding to density changes, we created 3-D wedge
models by changing vuggy zone thickness and the ratio of interparticle
porosity and vuggy porosity within the zone, assuming the same host-rock
condition. We then estimated seismic sensitivity by calculating the vuggy
porosity ranges that can be detected reliably from amplitude measured
in a noisy data set. Major conclusions are (1) seismic sensitivity of
vuggy porosity is controlled by rock physics, stratal geometry, seismic
frequency, and data quality, (2) a highly vuggy zone behaves similarly
to a tight zone seismically, (3) amplitude anomaly created by a 10-ft
vuggy zone should be detectable in 60-Hz, fair-quality (S/N=10) seismic
data, and (4) with good well control that reduces the ambiguity in total
porosity and thickness estimation, it should be possible to map the vuggy
zone by conducting seismic inversion. |