Fundamentals of Stratigraphic Interpretation of Seismic Data
Stratigraphic conclusions from seismic data depend on the data being sufficiently free of noise so that the seismic response is predominantly that of the sediments. Thus good recording and processing are essential. Given a reasonably noise-free response, seismic wavelength limits the detail which can be seen in two dimensions: vertical, or the thickness of Stratigraphic units; and horizontal, or the areal size of features.
Most reflection events seen on a seismic section are composites of reflections from individual interfaces. Calculating the waveform from a sequence of interfaces helps in understanding and interpreting waveform shape. This process is called synthetic seismogram construction where the input information is derived from well logs, and modeling where lateral variation is the principal concern. A comparison between synthetic seismograms and well logs illustrates the resolving power of seismic data and the limitations in trying to invert the process and derive logs from seismic data—thus, the seismic log process. The ease with which Stratigraphic significance can be derived from seismic data also depends on the type of display; those which enhance different aspects of data are helpful in appreciating geologic significance.
Figures & Tables
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.