--> Abstract: Late Cretaceous Play Types in the Southern Great Plains – Boldly Going Where All Silt Has Gone Before, by Tobias H. D. Payenberg, Karsten Schjoedt Nielsen, and Per Kent Pedersen; #90039 (2005)

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Late Cretaceous Play Types in the Southern Great Plains – Boldly Going Where All Silt Has Gone Before

Tobias H. D. Payenberg1, Karsten Schjoedt Nielsen2, and Per Kent Pedersen3
1 Australian School of Petroleum, Univeristy of Adelaide, Adelaide, Australia
2 Apache Canada Ltd, Calgary
3 Saskatchewan Industry and Resources, Regina, SK

The non-marine to shelfal deposits of the Late Cretaceous Niobrara and Milk River/Eagle formations include some of the most prolific gas reservoirs in Southern Alberta, Saskatchewan and Northern Montana. Clean Eagle Formation sandstones in northern Montana have produced more than 400 BCF in structural traps, while shaley shelf sandstones and siltstones of the Medicine Hat and Alderson members have produced more than 15 TCF from unconventional reservoirs to date. As gas in both, conventional and unconventional reservoirs, is biogenic in origin, source and migration are less important than reservoir and seal distribution. Therefore, for the successful exploration for these hydrocarbons, it is crucial to have a detailed understanding of the sedimentology and stratigraphy of the reservoir intervals on a local and regional scale.

Apart from conventional structural and partly stratigraphic plays in Eagle/Milk River sandstones, gas production from muddy sandstones of the Alderson Member is mainly from large continuous type gas accumulation, the classic, shallow unconventional gas plays. However, several very prolific gas accumulations have recently been discovered in stratigraphic and structural plays within thin bedded reservoirs. These are located basinward of the previous mapped boundary for economic gas production, highlighting the complexity of exploration for these plays.

Detailed sequence stratigraphic mapping using densely spaced wire-line log, core, and seismic data is the only way to delineate unconventional plays. In the case of the Niobrara Formation, for example, thirteen sandstones were mapped out using this technique, as opposed to the previously known three sandstones using lithostratigraphy.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005