YOUNG, S. S.1, D. D. POLLARD1, R. K. DAVIES2, D. L. VAN NOSTRAND3, and R. W. KRANTZ3
1Stanford Rock
Fracture Project, Stanford University, CA
2ARCO Exploration
and Production Tech., Plano, TX
3ARCO Alaska, Anchorage, AK
Abstract: Improving Seismic Interpretations
of Normal Fault
Geometries with Dislocation Models
To reduce the uncertainty associated
with interpreting fault
geometries in 3D seismic data, we use numerical
models to reproduce the displacement fields around a set of faults interpreted
in a 3D seismic data set from Prudhoe Bay, Alaska. The 3D seismic data,
along with log data from producing wells provide good constraints on
fault
geometry, slip distribution, and the geometry of sedimentary horizons near
the upper terminations of the faults. However, at greater depths, interpretations
become increasingly more subjective due to stratigraphic heterogeneity
and decreasing data quality. Consequently, the depth of a horizon near
a
fault
may be poorly constrained except where a well penetrates the given
horizon. To address this problem displacement fields are computed with
Poly3D, a 3D boundary element code that uses angular dislocations to approximate
faults in an elastic half space. Vertical displacement fields on horizontal
sections are used to construct synthetic structure contour maps, which
are compared to structure contours interpreted from seismic data. Parameters
that affect the modeled displacement fields include
fault
geometry and
slip distributions. Refinements to the original
fault
geometries are made
by varying these parameters until the synthetic structure contour map is
sufficiently close to the interpreted map. The imposed boundary conditions
take into account the tectonic history of the region, in particular the
depth of faulting and the regional strain orientation. The results from
this study indicate that dislocation models are an effective tool for improving
seismic interpretations of normal faults.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas