Seismic attributes in geological interpretation
| Exploring for Oil and Gas Traps | |
| |
| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Predicting the occurrence of oil and gas traps |
| Chapter | Interpreting 3-D seismic data |
| Author | Geoffrey A. Dorn |
| Link | Web page |
| Store | AAPG Store |
Rules of thumb
Here are a few rules of thumb that the interpreter should apply when approaching the use of attributes in a 3-D seismic survey:
- Consider the geology.
- Use different attributes.
- Use normalized attributes
- Avoid using an interval attribute that involves the summation of a data measure that varies in a cyclic fashion over an interval
Consider the geology
Consider the geological feature you are hoping to interpret and how varying that aspect of the geology might affect the seismic data. This can help guide the initial selection of attributes and will certainly help with interpreting the resulting data.
Using different attributes
Don't forget about using other attributes. It is not uncommon for there to be surprises in the data—unforeseen relationships that make physical sense once they have been discovered.
Normalized attributes
Be wary of using volume or interval attributes that are not normalized by the isochron of the interval over which they are calculated. This normalization can take the form of dividing the attribute by either the actual isochron or by the number of time samples in the interval. Although this normalization is not appropriate for some interval attributes (e.g., the maximum absolute amplitude in the interval), it is essential for any attribute that involves a summation over the interval. Without the normalization, the lateral attribute variation may simply be showing the variation in the isochron.
Cyclic variation of an attribute
Avoid using an interval attribute that involves the summation of a data measure that varies in a cyclic fashion over an interval. For example, in several systems it is possible to calculate the sum of trace amplitude over a user-specified interval. Since the trace amplitude has both positive and negative values over most intervals (unless the interval is so small as to include only a half-cycle of the data), the positive and negative values tend to cancel each other out. A second example would be the sum of instantaneous phase over an interval in the volume
Know the attribute
To apply these rules to attribute interpretation, it is essential for the interpreter to understand what the attribute is measuring in the data—the equation for the attribute. The only way the interpreter can know this is for the software vendor to provide well-written documentation, either on paper or online, that explains the mathematical calculation involved in generating the attribute. This combination—an interest on the part of the interpreter to understand the attributes and a willingness on the part of the vendor to provide that information—is essential to the intelligent and effective use of attributes in 3-D interpretation.
See also
External links
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