|KGS Open-file Report 2002-49|
Seismic Attributes for the Explorationist
by Susan E. Nissen
Open-file Report No. 2002-49
What are Seismic Attributes?"Seismic Attributes are all the information obtained from seismic data, either by direct measurements or by logical or experience based reasoning." (Taner, 2000)
Seismic attributes typically provide information relating to the amplitude, shape, and/or position of the seismic waveform.
Families of Attributes (based on method of generation)Complex Trace Attributes--The seismic data is treated as an analytic trace, which contains both real and imaginary parts. Various amplitude, phase, and frequency attributes can be calculated. Includes:
Figure 1. Complex Trace Attributes.
Fourier Attributes--frequency domain attributes obtained through Fourier analysis (e.g., amplitude variation with bandwidth in frequency (avbf), spectral decomposition)
Figure 2. Fourier Attributes.
Time Attributes--related to the vertical position of the waveform in the seismic section (e.g., horizon time picks, isochrons)
Window Attributes--attributes which summarize information from a vertical window of data.
Multi-trace Attributes--attributes calculated using more than one input seismic trace, which provide quantitative information about lateral variations in the seismic data (e.g., coherence, dip/azimuth)
Definitions of selected attributes
Figure 3. Instantaneous Attributes.
Response Attributes of shaded areaResponse Amplitude: maximum envelope
Response Phase: value of instantaneous phase at time of maximum envelope
Response Frequency: value of instantaneous frequency at time of maximum envelope
Figure 4. Response Attributes of shaded area.
Spectral DecompositionUses the Fourier transform to calculate the amplitude spectrum of a short time window covering the zone of interest.
The amplitude spectrum is tuned by the geologic units within the analysis window, so that units with different rock properties and/or thickness will exhibit different amplitude responses.
Figure 5. Spectral Decomposition.
Seismic CoherenceSeismic Coherence is a measure of the trace-to-trace similarity of the seismic waveform within a small analysis window.
Figure 6. Seismic Coherence.
What physical information is provided by these attributes?Envelope--presence of gas (bright spots), thin-bed tuning effects, lithology changes
Phase--lateral continuity of reflectors, bedding configurations
Frequency--bed thickness, presence of hydrocarbons, fracture zones
Spectral Decomposition--bed thickness
Coherence--faults, fractures, lateral stratigraphic discontinuities
How can I generate attributes?Most workstation-based seismic interpretation systems have tools for generating a suite of complex trace attributes. The KINGDOM Suite, a PC-based interpretation system from Seismic Micro-Technology, Inc., was used to generate the attributes for this presentation.
Spectral decomposition is a part of the OpenSEIS processing system, available for Unix and Linux platforms from OpenGeoSolutions.
Coherence CubeTM processing can be obtained from Scott Pickford. There are also several software products available which calculate coherence-type attributes (e.g., Variance Cube fromGeoQuest or PostStack ESP from Landmark).
Methods of interpreting attributesIdentify spatial patterns/trends in attribute data
Tie attributes to well control using statistical methods (e.g., crossplots)
Automatically analyze multiple attributes (with or without well control)
Kansas Geological Survey
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Updated Nov. 25, 2002
URL = http://www.kgs.ku.edu/PRS/publication/2002/ofr49/index.html