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Geophysical Imaging For Contaminated Site Characterization
Yoram N. Rubin, University of California, Berkeley
Nadim Copty, University of California, Berkeley
Sibyl Leigh, University of California, Berkeley
UC Water Resources Center Technical Completion Report W-782
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ABSTRACT: The analysis and management of groundwater flow problems often involve the
prediction of fluid flow and/or contaminant migration patterns. These phenomena, however,
are strongly influenced by the heterogeneity of the hydrogeological properties of the
soil. The purpose of this project is to derive joint geophysical-hydrogeological procedures
for the characterization of subsurface flow parameters. The first part of this study presents
a formal stochastic approach for the integration of surface seismic data and well data into
the identification of the spatial arrangement- location, geometry, and interconnectedness of
lithofacies. Towards this goal, the lithology of the subsurface is represented through a
random indicator function whose spatial structure is identified from seismic reflection data
and well logs. Seismic interval velocities and measures of their uncertainties are computed
from normal moveout corrections to the seismic reflection data. Calibration curves constructed
from the well logs transform these velocity estimates into a lithology indicator
prior probability field. From the well data and the prior probability field, the indicator
covariance function and its associated confidence limits are computed. Neighboring lithology
logs and the indicator covariance function are then combined to update the indicator
probability field. To illustrate the applicability of the proposed characterization procedure,
a semi-synthetic case study- based on the Fremont study area near the city of Fremont,
California- is performed.
In the second part of this study, a Bayesian method is developed to estimate the
spatial distribution of the permeability. In addition to sparsely sampled permeability and
pressure data, the proposed approach incorporates densely sampled seismic velocity data
along with semi-empirical relationships between seismic velocity, permeability and pressure.
A hydrological inversion is first performed, based solely on the permeability and pressure
data. In light of the available seismic data, the velocity-permeability-pressure relationships are then used to update, in a Bayesian sense, the image of the permeability field. To demonstrate
the usefulness of this approach, synthetic case studies are performed. For further
validation, the proposed methodology is applied to real data collected at Kesterson Reservoir,
California. These studies demonstrate that by joining seismic data and hydrological
data into a common inverse procedure, improved permeability images can be reproduced.
SUGGESTED CITATION:
Yoram N. Rubin, Nadim Copty, and Sibyl Leigh,
"Geophysical Imaging For Contaminated Site Characterization"
(December 1, 1994).
University of California Water Resources Center.
Technical Completion Reports.
Paper 782.
http://repositories.cdlib.org/wrc/tcr/782
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