Date of Award
Master of Science (MS)
The carbonate Wayne beds of the Frobisher-Alida interval (Mississippian Mission Canyon Formation) in the Williston Basin, North Dakota, are capable of producing as much as 400,000 barrels of oil per well at depths of only 3,100 feet. Wayne production is from structural traps in the intertidal packstone-wackestone lithofacies; however, the ultimate recoverable reserves of oil per well is controlled neither by structure, nor by depositional environments.
The Wayne beds underwent cementation and micritization in the marine phreatic diagenetic environment. Hypersaline diagenesis caused minor dolomitization and anhydritization. Dissolution and minor cementation occurred in the freshwater vadose zone. Freshwater phreatic diagenesis resulted in mineralogical stabilization and minor cementation. Compaction, pressure solution, dolomite and calcite cementation, and anhydritization occurred in the burial diagenetic environment.
Depleted o13C in the carbonates immediately below the pre-Mesozoic unconformity surface suggests that vugular and solution-enlarged porosity formed in the freshwater vadose zone. Beneath paleoislands, mineralogical stabilization in the freshwater phreatic zone prevented later porosity reduction by compaction or cementation. On the flanks of the paleoislands and in paleolows, porosity was occluded by dolomite and calcite cement. The dolomite cement has 6180 consistent with a burial diagenesis origin. Permeability reduction by pore-bridging anhydrite cements post-date the pore-occluding dolomites. Wayne beds contain much less pore-bridging anhydrite beneath paleohighs where the overlying Glenburn evaporites were removed due to erosion than beneath paleolows where the Glenburn is still present. Sulfur stable-isotope data suggest that the sulfur in these pore-bridging anhydrites originated in the Glenburn evaporites.
The amount of Wayne oil production from structural traps in the study area is controlled by diagenetic rather than depositional features. Porosity was occluded by burial dolomite and calcite cements in paleolows. Permeability was reduced by burial anhydrite cements in localities where the Glenburn has not been eroded. Thus, the best production within a field comes from those portions of the reservoir which were once beneath islands and/or eroded highs.
Wetmore, Michael M., "Diagenetic controls of reservoir quality in the Mississippian Wayne Beds in the Williston Basin, Bottineau County, North Dakota" (1994). Theses and Dissertations. 320.