PARRA, J. O.1, C. L. HACKERT1, R. L. BROWN2, and H. A. COLLIER3
1Southwest Research
Institute, San Antonio, TX
2Oklahoma Geological Survey, Norman,
OK
3Collier Consulting, Stephenville, TX
Abstract: An Approach to Predict Elastic Scattering and Intrinsic Attenuation in Turbidites at the Buena Vista Hills Field, California
Attenuation of seismic energy and velocity
anisotropy consists of an intrinsic component and an apparent component
caused by strictly elastic scattering from velocity and density heterogeneities.
The intrinsic component of attenuation is believed to be related to fluid
properties in the porous portions of a reservoir. However, it may be difficult
to distinguish between the apparent effects caused by elastic scattering
and the intrinsic effects when both mechanisms are operative. In this case,
a detailed velocity model of the formation is required in order to predict
the elastic scattering component of velocity We have implemented such a
scattering correction technique to determine the magnitude of the intrinsic
attenuation from observed sonic velocity data. We constructed a highresolution
velocity model with layers one inch thick based on FMI logs and quality
factors derived from sonic log data recorded at the Buena Vista Hills (BVH)
field. Quality factors for intervals were derived using the two station
spectral ratio method applied to the full wave sonic log data at the BVH
field. The wave response for intervals at different frequencies was obtained
using a viscoelastic plane-wave modeling code to model a finely layered
region. Intrinsic attenuation is determined in one way by measuring amplitudes
of sonic full wave seismograms. The amplitudes at two adjacent stations
are processed using the spectral ratio method to obtain an estimate of
the attenuation. The resulting difference between the observed velocity
and the velocity predicted as a result of elastic scattering is assumed
to be due to intrinsic attenuation. The applicability of this method is
demonstrated by comparing the predicted intrinsic attenuation results,
with the intrinsic attenuation determined from sonic logs.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas