ABSTRACT: Stratigraphy and Diagenesis of the Bakken Formation, West Central Saskatchewan

KASPER, DANA L., H. E. HENDRY, and R. W. RENAUT, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

The Upper Devonian-Lower Mississippian Bakken Formation of the Williston basin is a widespread, predominantly siliciclastic unit whose lithostratigraphic equivalents cover some two-thirds of the North American craton. The radioactive nature of both the upper and lower shale members makes them useful as subsurface markers, and they are known source rocks with up to 15% TOC. The middle sandstone member is a heavy oil producer in the study area of west-central Saskatchewan (16 degrees API and up to 30% porosity).

Core and well log data were used to identify six lithofacies within the Bakken: (1) black shale; (2) bioturbated siltstone; (3) thin-bedded bioturbated sandstone; (4) thin-bedded sandstone; (5) interbedded sandstone-siltstone-shale; and (6) oolitic-bioclastic grainstone.

The Bakken was deposited on a drowned shelf at a time when sea level and oxygen content of the water column fluctuated during an overall relative sea level rise. Both shale members represent deposition of fine-grained sediments under dysaerobic to anaerobic conditions. In contrast to earlier tidal interpretations, the middle sandstone member accumulated during a regressive pulse when storms were responsible for transportation and deposition of sediments.

Calcite cementation in the middle sandstone member obliterated most primary porosity during burial prior to significant compaction. Subsequent reservoir formation, a result of calcite leaching, created secondary porosity of up to 30%, which developed in linear bodies of clean, mature, thin-bedded sandstone.

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