Application of Seismic Reflection Configuration to Stratigraphic Interpretation
Seismic stratigraphy is basically a geologic approach to the Stratigraphic interpretation of seismic data. The unique properties of seismic reflections allow the direct application of geologic concepts based on physical stratigraphy. Primary seismic reflections are generated by physical surfaces in the rocks, consisting mainly of stratal (bedding) surfaces and unconformities with velocity- density contrasts. Therefore, primary seismic reflections parallel stratal surfaces and unconformities. Whereas all the rocks above a stratal or uniformity surface are younger than those below it, the resulting seismic section is a record of the chronostratigraphic (time-stratigraphic) depositional and structural patterns and not a record of the time-transgressive lithostratigraphy (rock-stratigraphy).
Because seismic reflections follow chronostratigraphic correlations, it is not only possible to interpret postdepositional structural deformation, but also it is possible to make the following types of Stratigraphic interpretations from the geometry of seismic reflection correlation patterns: (1) geologic time correlations, (2) definition of genetic depositional units, (3) thickness and depositional environment of genetic units, (4) paleobathymetry, (5) burial history, (6) relief and topography on unconformities, and (7) paleogeography and geologic history when combined with geologic data. However, one limiting factor is that lithofacies and rock type can not be determined directly from the geometry of reflection correlation patterns.
To accomplish the geologic objectives just listed, we recommend the following three-step interpretational procedure: (1) seismic sequence analysis; (2) seismic facies analysis; and (3) analysis of relative changes of sea level.
Seismic sequence analysis is based on the identification of stratigraphic units composed of a relatively conformable succession
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Papers from a research symposium at the 1975 American Association of Petroleum Geologists and supplemented by later reports became “Seismic Stratigraphy Applications to Hydrocarbon Exploration”, one of AAPG’s best-selling book publications. Dramatic improvements in seismic imaging were demonstrated, a result of developments in seismic data quality and the processing capability of electronic technology. Twenty-eight articles are grouped into three sections. The first describes principles that both permit and also limit interpretations. The second section presents sixteen articles that describe the qualitative approach to stratigraphic interpretations of reflection records, and the final section presents techniques and examples of modeling. Of particular interest are a series of eleven papers in the second section under the subject heading of “Seismic stratigraphy and global changes of sea level”. Prepared by P. R. Vail, R. M. Mitchum and others from Exxon, they describe the regional unconformities and stratigraphic changes resulting from sea level fluctuations, and the manner in which these changes can be interpreted from seismic surveys. For many individuals within the oil industry who purchased this book, it was their first introduction to the modern concept of sequence stratigraphy that would have a major impact on the methodology of petroleum exploration.