Seismic sequence analysis

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Exploring for stratigraphic traps
Author John C. Dolson, Mike S. Bahorich, Rick C. Tobin, Edward A. Beaumont, Louis J. Terlikoski, Michael L. Hendricks
Link Web page
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Objective

The objective of seismic sequence analysis is to identify depositional sequences and systems tracts on seismic sections by interpreting the location of their boundaries. Boundaries are manifested as discontinuities in seismic sections and are located mainly by finding reflection terminations.[1]

Procedure

Follow the steps listed below to perform a sequence analysis of a seismic section (adapted from Vail[1]).

  1. Look for places where two reflectors converge. Where reflectors converge, there will be terminations.
  2. Mark the reflection terminations with arrows.
  3. Draw in the discontinuity surface between the onlapping and downlapping reflections above, and the truncating and toplapping reflectors above. If the discontinuity surface becomes conformable, trace its position across the section by reflection correlation.
  4. Continue the process described in steps 1, 2, and 3 for all the seismic lines in the grid.
  5. Close all seismic grid loops by checking the loop ties for each discontinuity or its correlative equivalent.
  6. Categorize each discontinuity.
    • If it is characterized by regional onlap above and truncation below then it is probably a sequence boundary
    • If it is characterized by regional downlap then it is most likely a downlap surface

Marking a seismic section, marking

The table below shows suggested colors for marking seismic sections during sequence analysis (after Vail[1]).

Feature Color
Reflection terminations and reflection patterns Red
Downlap surfaces Green
Transgressive surfaces Blue
Sequence boundaries Miscellaneous

Reflection terminations

The table below groups termination patterns by position with respect to a discontinuity.

Reflection termination point Pattern Associated discontinuity
Above a discontinuity Onlap Sequence boundary (unconformity)
Downlap Downlap surface (condensed section)
Below a discontinuity Truncation Sequence boundary
Toplap Sequence boundary
Apparent truncation Downlap surface

Locating reflection terminations

Figure 1 Reflection termination patterns and the associated discontinuity surfaces.

Locating reflection termination is a matter of finding the patterns described in the table above. Figure 1 shows these patterns and the associated discontinuity surfaces.

See also

References

  1. 1.0 1.1 1.2 Vail, P. R., 1987, Seismic stratigraphy interpretation procedure, in Bally, A. W., ed., Atlas of Seismic Stratigraphy: AAPG Studies in Geology No. 27, p. 2.

External links

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Seismic sequence analysis
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