interpretation is a cornerstone of our industry, as interpretation
success has grown increasingly dependent on ever-newer combinations
of seismic attributes (SAs).
are simply defined as information extracted or computed from seismic
data. What combinations work best depend on reservoir characteristics,
the available data and, most importantly, human expertise.
attributes are not magic, but the explosion of 3-D seismic at the
end of the 20th century resulted in dramatic increases in the types,
combinations and uses of SAs. We now have available multi-trace,
pre-stack, horizon, wavelet and 4-D attributes in addition to those
derived from shear wave volumes. These allowed for significant improvements
in estimates of reservoir properties from seismic (RPFS).
table defines terms used in seismic attribute analysis today.
of potentially useful attributes requires seismic interpreters to
keep current and to have the most effective efficient "fit for purpose"
work flows. One important aspect of these work flows is "starting
with the end in mind." For example, if amplitudes or wide azimuths
are critical, the seismic acquisition and processing for those SAs
should be optimized.
the potential for abusing seismic attributes also has increased.
One common abuse of seismic attributes often occurs "because it's
there." Interpreters today have access to many SAs on their workstations,
but often have very little time to properly understand these attributes,
model them and correctly correlate them with ground truth and the
principles of physics.
of pretty SAs that are not well understood. This can damage your
credibility while tarnishing the true potential of SAs. Don't expect
your workstation to pop out the solution.
of "black box" answers. Instead, commit the resources to correlate,
model and understand your SAs, and what they can and cannot do.
now make it very easy to generate, for example, the third derivative
of the instantaneous phase or the second derivative of instantaneous
frequency. Even if this SA correlates with ground truth somehow,
will you understand it or trust its significance?
abused shortcut often sounds like: "Just give me the one attribute
that solves my problem."
unusual areas, interpreters have been able to succeed using only
a single attribute interpretation. However, I have not yet found
an area where a single attribute provides the optimum answer.
figure 2 how none of the four attributes alone show the sand channel
very well -- but when they are combined, the result is both quantitatively
and areally more accurate than any individual attribute.
shows the dramatic potential of SAs for lithology prediction. We
add value by using experience to improve estimates of reservoir
properties from seismic (RPFS), reducing risk and helping to quantify
avoid grabbing the first attribute(s) that seems to work.
develop a robust, efficient work flow that quickly considers many
of the most promising attributes and objectively correlates them
with seismically scaled and corrected ground truth. Then model these
attributes to understand and optimally guide the SA combination
to best estimate the reservoir properties, and quantify the uncertainty
of those estimates.
also a real danger of using too many SAs to "over-fit" the data.
With unlimited attributes -- and therefore unlimited degrees of
freedom -- statistical accidents will occur. The critical step is
testing for significance -- for example, by blindly dropping one
well or zone at a time. The number of attributes ideal for reservoir
property estimation typically varies from two to four, depending
on the area, data and objective.
the pitfalls in seismic attribute analysis (SAA), there are many
successful examples of predicting RPFS. For example, consider figure
2: It is often important and valuable to define the 3-D extent of
a channel or sand body. Figure 2 shows an example of combining four
3-D attribute volumes along with the appropriate well information
to predict lithology.
optimized your SAA workflow, it can dramatically improve property
and risk estimates. Robust work flows have been developed on data
sets around the world, in clastic and carbonate environments, onshore
and offshore. The accuracy of estimates varies with location, data
quality and objectives.
and accuracy of reservoir modeling and simulation has also been
improved using RPFS estimates and associated uncertainty cubes.
Keep up-to-date on seismic attributes, SA analysis and work flows.
and scale well data to ensure appropriate ground truth ties to
the seismic, including positioning, scaling, wavelet and phase
the physics and significance of SAs by forward modeling. For example,
testing the sensitivity to varying thickness or fluid substitution.
known abuses or pitfalls, including assuming well data is ground
truth; sloppy ties; "because it's there"; black boxes; endless
SA derivatives; single attribute obsession; over-fitting; and
not blind testing for significance.
the most useful SAs, input cubes and SAA methods for your objectives,
and how accurate your RPFS estimates are.
your critical SAs, when appropriate, by acquiring/processing 3-D
uncertainty via uncertainty cubes.