The capability, as of the late 1960s, of the seismic reflection method for the location of stratigraphically entrapped hydrocarbons was evaluated by Lyons and Dobrin. Limitations of the data resolution that could be expected from seismic reflection made it appear unlikely that significant improvement could be expected in its historically poor performance as a tool for finding Stratigraphic oil and gas.
Since that time, significant developments in seismic data acquisition and processing have resulted in better definition and hence resolution of the basic seismic signal. Among these developments are the use of seismic amplitudes in defining Stratigraphic features. Model studies and tests in areas where the geology is known give encouraging indications that these developments should improve the effectiveness of seismic reflection techniques. But we still have no way of knowing whether these capabilities overcome limitations of the method to the extent that discovering Stratigraphic accumulations of hydrocarbons has actually been improved. It is hard to assess the value of geophysical data in Stratigraphic discoveries that have involved extensive coordination of geophysics and geology. Moreover, few case histories are available on discoveries where the most modern seismic techniques have been used.
Recent interpretive techniques developed by Vail et al enable us to recreate depositional history and deduce depositional environments by analysis of reflection patterns on record sections. Such analysis can isolate areas that are environmentally most prospective for hydrocarbon accumulation, making it possible to locate Stratigraphic entrapments with a minimum of additional seismic and geologic investigations.
Where technological improvements have increased the potential of the reflection method for finding Stratigraphic oil and gas directly, there still exists a need for sophisticated integration of seismic and geologic data, particularly from wells that correlate with seismic lines. Most important discoveries of Stratigraphic oil and gas (attributable to seismic reflection) have used such integration— many with seismic data that are considered primitive by today’s standards.
Case histories present the performance of seismic reflection in exploring for various types of Stratigraphic entrapment features, including carbonate bodies, truncations of clastic layers, sandstone bodies, and facies transitions.
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.