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GCCorendering – A Powerful Tool for Mapping Faults*
Alexandra Kirshner1 and Bruce Hart2
Search and Discovery Article #40431 (2009)
Posted September 22, 2009
*Adapted from the Geophysical Corner column, prepared by the authors, in AAPG Explorer, June, 2009, and entitled “A Powerful Tool for Mapping Faults”. Editor of Geophysical Corner is Bob A. Hardage (mailto:[email protected]). Managing Editor of AAPG Explorer is Vern Stefanic; Larry Nation is Communications Director.
1Graduate student, Rice University, Houston, TX ([email protected])
2Director of Shale, Seal and Pressure Systems, ConocoPhillips, Houston, TX ([email protected])
High-resolution 3-D seismic
data
provide geoscientists
with tremendous opportunities to study subsurface structure and stratigraphy.
When used appropriately, the visualization tools provided by
seismic
interpretation
software packages facilitate structural interpretations and
provide insights to relationships and features that otherwise might be hidden.
In this column we illustrate the use of a technique known as corendering to
assist fault interpretations in a structurally complex area. Simply stated,
corendering is a computer graphics tool that allows an interpreter to view two
data
volumes simultaneously.
Many seismic
interpreters continue to use amplitude
volumes for fault
interpretation
. They use reflection terminations, reflection
offsets, changes of dip and other lines of evidence to identify faults.
Coherency and related attributes such as semblance quantify differences in
trace shape between traces in a 3-D
seismic
survey. Simplistically, high
coherency values correspond to laterally continuous reflections, whereas low
coherency values are associated with sharp boundaries, such as those associated
with faults, channel margins and other features. Although coherency volumes are
commonly examined alone for fault mapping, the simultaneous display of coherency
and amplitude volumes through corendering can be a powerful tool for
identifying and mapping faults. The images presented here combine those two
volumes by using color (conventional blue-white-red color bar) to display the
amplitude information and shading (as if a light were shining on the
data
) to
display the coherency attribute.
|
A 300-square-kilometer 3-D
A series of normal faults affects Cretaceous strata, but few of these faults extend down into the Jurassic and underlying strata. Furthermore, most of these normal faults terminate upward at a Paleocene unconformity. The basin geometry is controlled by a normal fault that strikes approximately NW-SE. The survey area contains three families of faults that trend roughly parallel to the principal fault. These fault families contain segmented normal faults, both with splays of the same family and between differently oriented families.
Figure 1a
shows an arbitrary vertical transect and intersecting timeslice that
illustrate the expression of the faults in the amplitude
Similar corendered
Picking faults in a 3-D
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