Sequence Stratigraphy Past, Present and Future; and the Current Role of 3D Seismic Data

Henry W. Posamentier: Anadarko Canada Corporation, Calgary, Alberta

Abstract

In the twenty-five years since the landmark publication of AAPG Memoir 26, the concepts of sequence stratigraphy have evolved rapidly. This discipline, an outgrowth of seismic stratigraphy, has spread far beyond applications to 2D seismic data alone, embracing data sets ranging from biostratigraphic to geochemical to physical oceanographic and from borehole to outcrop, and finally, coming full cycle, to 3D seismic data. Initially the domain of industry geoscientists, sequence stratigraphy has gained widespread acceptance among geoscientists in all professions, having been recognized as a discipline that facilitates integration of a broad range of disciplines.

The evolution of sequence stratigraphic concepts is far from complete. In particular, recent increased availability of high-quality 3D seismic coverage promises to provide insights that will lead to further modification of sequence concepts. The obvious advantage of 3D seismic coverage, in addition to enhanced 2D profiles, is that they afford exceptional plan views of the subsurface that in the past could only be inferred. These plan view images now comprise a fundamental starting point from which geologic analyses and interpretation can begin. Such images depict paleo-landscapes, which can be analyzed using time-honored principles of geomorphology, leading to the development of the discipline of seismic geomorphology. When used in conjunction with seismic stratigraphy, seismic geomorphology can significantly enhance sequence stratigraphic interpretations.

The identification of depositional elements such as channels, valleys, shorefaces, shelf ridges, etc., in plan view can be integrated with seismic stratigraphic analyses of associated seismic profiles to calibrate profile reflection patterns and refine analyses of basin fill histories. Systematic seismic geomorphologic analysis of 3D seismic volumes can bring to light spatial and temporal relationships of successive depositional systems. Recognition of these systems and analyses of their succession can help in the identification of possible missing facies tracts. This, coupled with direct and indirect recognition of unconformities, comprises an integral aspect of sequence stratigraphic interpretation.

In certain instances, 3D seismic data can lead to the direct identification of previously unrecognized depositional features. An example of such a feature is the shelf ridge; though common in modern settings, few documented studies of unequivocal ancient examples have appeared in the published literature. Direct imaging of such features in the subsurface using 3D seismic data, integrated with core observations, have lead to the conclusion that such deposits can comprise a significant component of the transgressive systems tract. This constitutes an example of a refinement of the general sequence stratigraphic model. In this example, also, seismic geomorphologic analyses have provided key insights with regard to the issue of preservation potential of a type of feature well known in modern environments but thought to have little chance of surviving subsequent erosional events and being preserved in ancient sections.

Revitalization and continued evolution of sequence stratigraphic concepts will occur through the integration of such disciplines as seismic geomorphology, seismic stratigraphy, biostratigraphy, and chemostratigraphy. Because of the inherent flexibility imbedded into these concepts, sequence stratigraphy remains evergreen and continually evolving. Moreover, the development of scientific analyses based on new types of data that we cannot even now anticipate assures us that sequence stratigraphy will continue to evolve and be refined well into the future and remain a backbone for the study of sedimentary rocks.