--> Abstract: Oolite and Back-Barrier Reservoir Facies in the Mississippian Midale Beds, Southeastern Saskatchewan: Not Another Subcrop Play, by Andrew Rene Nimegeers; #90039 (2005)

Datapages, Inc.Print this page

Oolite and Back-Barrier Reservoir Facies in the Mississippian Midale Beds, Southeastern Saskatchewan: Not Another Subcrop Play

Andrew Rene Nimegeers
Saskatchewan Industry and Resources, Regina, SK

Most hydrocarbon production along the prolific Midale-Steelman oilfield trend of southeastern Saskatchewan is related to oil trapped beneath a sub-Mesozoic unconformity surface. In the West Kingsford Field, however, hydrocarbon entrapment in oolite and dolo-wackestone reservoirs of the Mississippian (Osagian) Midale Beds results from lateral and vertical facies changes into non-porous limestones. These complex facies relationships can only be identified and mapped through detailed core and geophysical well log analysis.

Oolitic grainstones and packstones of the Midale Beds were deposited as shore-parallel shoals and barrier-islands in a shallow inner ramp setting along the northern margin of the Williston Basin. In the West Kingsford Field, oolitic limestones are interbedded with non-porous, peloidal-algal packstones and wackestones. Facies associations suggest the shoals developed in a storm-influenced, but otherwise, protected ramp setting. Vertical relief across the shoals relative to adjacent lagoonal facies rarely exceeded 3 m. The oolites were preferentially deposited along the seaward flanks of a paleotopographic ridge where abrupt thickness and lateral facies changes occur in the Midale and underlying Frobisher Beds. Following a sea-level fall that exposed the oolitic shoals, transgression deposited bioclastic back-barrier fans on the leeward sides of the shoals. A porous dolo-wackestone facies is interbedded with these back-barrier sands and produces hydrocarbons in the West Kingsford Field. The wackestone reservoir thins and onlaps underlying lagoonal facies in a landward direction. Significant potential exists for similar Mississippian plays in southeastern Saskatchewan where facies transitions from shoal/barrier to back-barrier environments occur.

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