Search

Winnipegosis (Middle Devonian) pinnacle reefs have been a major exploration target within the southern Elk Point Basin for over 20 years. To date, ten pinnacle reefs have been drilled in North Dakota with commercial quantities of oil being conspicuously absent. Many of these pinnacle reefs have excellent reservoir potential as indicated by the recent discovery of the Home-Tableland reef in southeastern Saskatchewan. The pinnacle reefs of this study show an overall, aggradational, shallowing-upward motif which suggests development during a relative rise in sea level. The shape, morphology, and overall extent of these reefs are related to the size, density, and bathymetry of the initiating mounds. Bio- and lithofacies evidence strongly indicates that most of these reefs grew to sea level and formed wave-resistant structures. The subsequent drop in sea level produced a succession of shallow water facies. Continued restriction of the basin subaerially exposed the tops of the pinnacles resulting in extensive vadose diagenesis. Both destructive and constructive diagenetic processes have influenced the present porosity and permeability of the pinnacle reefs. Dolomitization and degree of dissolution are the two most important factors controlling porosity development and these diagenetic processes are locally controlled by the depositional environment. The best reservoir quality rocks are found associated with the higher energy reefal lithofacies. [ABSTRACT FROM AUTHOR]