ABSTRACT: Applications of Siliciclastic Sequence Stratigraphy to Exploration and Production: Successes, Failures, and Future Directions

WEIMER, PAUL, and DAVID W. BOWEN, University of Colorado, Boulder, CO

The application of sequence stratigraphic concepts, first proposed during the mid-1970s, has led to both successes and failures in exploration and production. Although a broad spectrum of reservoir occurrences are predicted in siliciclastic sequence stratigraphic models, the most successful applications have been in incised-valley fills (lowstand and transgressive systems tracts), and in turbidite systems (lowstand systems tracts). Notable exploration failures have occurred also in these settings.

Incised-valley fill systems as exploration targets were first described by John Harms in 1966 for the Lower Cretaceous Muddy Formation of the eastern Denver basin. By the late 1970s, incised-valley plays became common exploration plays in many basins, primarily in the Rocky Mountains. Principal successful units of exploration were in the Morrow Formation (Pennsylvanian) in southeastern Colorado, the Muddy Formation (Lower Cretaceous) of Colorado and Wyoming, and similar age strata of the Viking Formation and equivalents of the Alberta basin. The main shortcomings in the exploration of incised valleys are: (1) locating the valley margin--valleys are narrow, linear to sinuous targets; (2) predicting the occurrence of sandstone- versus shale-dominated valley-fill; and (3) locating sandst ne reservoirs within sandstone-dominated valleys. Valley fill is highly variable and contains a wide variety of lithofacies associated with the infilling and backstepping of environments during the relative rise in sea level.

As deep-water exploration has increased throughout the 1980s, sequence stratigraphic concepts have had a major impact on the exploration of the lowstand systems tracts. Basin-floor fans and channel-levee systems of the slope fan have been major exploration targets with some notable successes throughout the world, primarily in the Eocene and Oligocene strata of the Campos basin (Brazil), and the Neogene strata of the northern Gulf of Mexico. Major failures have occurred in the drilling of seismic-defined mounds that are primarily shale and the drilling of amplitude anomalies associated with nonreservoir units.

Future exploration successes utilizing sequence concepts will occur with the further refinement and predictability of lowstand systems tracts (fans, valley fill, and lowstand shorelines). Application of sequence concepts will also have a major impact on reservoir development. Understanding stratal patterns and key surfaces and how they may serve as possible permeability barriers/flow retardants between lithofacies are critical to better reservoir development in the future.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)