Seismic Sequence Stratigraphy Technique On A 3D Workstation
Authors: Risch D.L. , Donaldson B.E. , Taylor C.K. 
Published: October 2008

A 3D seismic survey in the Green Canyon area of the northern Gulf of Mexico was interpreted for stratigraphy using a sequence stratigraphic analysis. The versatility of the workstation greatly increased our efficiency over manually interpreting 2D seismic paper sections. Compressed black and white variable density displays and narrow band yellow and green instantaneous phase displays were key factors in identifying and interpreting horizons and subtle stratigraphic features. The area-wide autotracking feature allowed the interpreter to pursue other tasks with acceptable map results. The increased spatial resolution of the 3D data over our 2D data grid allowed us to image the detailed geomorphic shape of a deep water Pleistocene slope fan channel/levee system with multiple flattened horizon slices. Lithofacies maps of the lowstand slope fan and prograding wedge were made in much less time than the manual method by using 3D volume attribute maps called reflection heterogeneity and reflection intensity.

INTRODUCTION

Seismic sequence stratigraphy has developed over the past few years as a significant exploration tool for the oil and gas industry. It is a model-based concept to interpret cyclic stratigraphy and predict lithofacies by integrating well logs, biostratigraphy and seismic data. We sought to extend our 2D interpretation experience to 3D datasets for improved lithofacies predictions through tighter seismic control and utilizing the capabilities of the interactive workstation. Nine federal lease blocks from a Green Canyon 3D seismic survey in the northern Gulf of Mexico were selected in an area where our 2D sequence stratigraphic interpretation could be used as a framework (Fig. 1). Water depths range from 2000'- 3000' in this region of the continental slope. Sequence boundaries were established and dated using seismic data and biostratigraphic data from six nearby wells. An early Pleistocene sequence (1.4- 1.1 million years) with a well developed slope fan was selected to evaluate and demonstrate identification of boundaries, autotracking capabilities and interval mapping, The deepwater sediments are predominantly lowstand slope fan (SF) and prograding wedge (PW) deposits.

PRINCIPLES OF SEQUENCE STRATIGRAPHY

A sedimentary sequence is composed of a group of genetically related sediments (facies) deposited during one cycle of relative sea level rise and fall. The components are three lowstand depositional complexes (basin floor fan, slope fan, prograding wedge), a transgressive systems tract and a highstand systems tract. Each systems tract and depositional complex has predictable lithofacies for each basin environment. These depositional units have diagnostic well log and seismic reflection characteristics. In addition, biostratigraphic data is used to date the sequences, interpret the paleo-environment and identify condensed section shales within a sequence. Hence, lithofacies can be predicted from an integrated interpretation of well logs, seismic and biostratigraphic data. Further discussions of sequence stratigraphy can be found in Van Wagoner, et al.1, Sangree, et al2, and Barnett3.