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GCThe Use and Abuse of Seismic Attributes*
By
Hans E. Sheline1
Search and Discovery Article #40143 (2005)
Posted March 1, 2005
*Adapted from the Geophysical Corner column in AAPG Explorer, January, 2005, entitled “Don’t Abuse Seismic Attributes” and prepared by the author. Appreciation is expressed to the author, to Alistar R. Brown, editor of Geophysical Corner, and to Larry Nation, AAPG Communications Director, for their support of this online version.
1VeriNova, Sugar Land, Texas ([email protected])
General Statement
Seismic interpretation is a cornerstone of our industry, as interpretation success has grown increasingly dependent on ever-newer combinations of seismic attributes (SAs). Attributes 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.
Seismic 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 (Figure 1). We now have available multi-trace, prestack, 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).
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Figure Captions and Table Caption
General Comments
Table 1 defines terms used in seismic
Unfortunately, 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 understand these attributes properly, model them, and correctly correlate them with ground truth and the principles of physics. Be wary 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. Be wary of “black box” answers. Instead, commit the resources to correlate, model, and understand your SAs and what they can and cannot do. Workstations 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?
Another abused shortcut often sounds like: “Just give me the one
Note in Figure 2 how none of the four
attributes alone shows the sand channel very well – but when they are
combined, the result is both quantitatively and areally more accurate
than any individual
Therefore, avoid grabbing the first There is 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.
Case History Example
Despite the pitfalls in seismic Once you have 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. The speed and accuracy of reservoir modeling and simulation have also been improved using RPFS estimates and associated uncertainty cubes.
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