Paleokarst Reservoirs of the Lower Carboniferous (Mississippian) Madison Group and Jura-Cretaceous Success Formation, West-Central Saskatchewan
Dan Kohlruss | Saskatchewan Geological Survey, Ministry of Energy and Resources
April 09, 2019 | 11:30 am doors open
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The Lower Carboniferous (Mississippian) Madison Group and the Jura-Cretaceous Success Formation in the Kindersley-Kerrobert area of west-central Saskatchewan combine to represent a significant paleokarst terrain. The marine Madison limestones were subjected to a long period of exposure, weathering and erosion resulting in substantial structural irregularity at its upper surface along with abundant decomposition of the limestones both at surface and below. The resulting karst byproduct is the primary mode in which the Success Formation formed within the study area. Previous work recognized the Success Formation was a result of karsting processes but did not identify any distinct facies, facies associations nor attempt detailed mapping. For the first time, this study has mapped the internal stratigraphy of the Success Formation’s karst facies and facies associations.
Analysis of drill cores, drill cutting samples and geophysical well logs within the study area resulted in the identification of six distinct recurring karst facies as well as four karst facies associations. The karst facies encountered are:
1) mudstone grading to matrix supported chert pebble conglomerate,
2) matrix-rich clast supported chaotic chert and sandstone breccia,
3) crackle breccia,
5) chaotic mud and chert rubble breccia/conglomerate, and
6) matrix-supported chaotic breccia.
The karst facies associations represented are:
1) collapsed cave,
2) preserved cave roof,
3) epikarst, and
4) soil breccia- karst paleosol.
The Success is a known heavy oil and natural gas producer and the production is sourced from two previously unrecognized, distinct and separate reservoirs. These correspond with the collapsed cave and epikarst facies associations. This was determined through analysis of cross-sections along with structure and isopach maps of the facies associations. These maps were analyzed alongside oil cut and gas production maps which identified discrete oil and gas traps within the two reservoirs. The traps include; structural closure related to the underlying Madison’s paleo-topography, and lateral pinch-outs of the two paleo karst reservoir facies associations.
Dan Kohlruss is a Senior Petroleum Research Geologist with the Saskatchewan Geological Survey. He received his B.Sc. and M.Sc. degrees at the University of Regina in 1997 and 2012 respectively. Beginning in 1998, Dan consulted as a well-site geologist throughout Alberta and Saskatchewan and then moved to Saskatchewan’s Department of Energy and Mines in 2001. Dan joined the Geological Survey in 2007 where his current research includes the study of karst features in the Madison Group and Success Formation as well as the study of clastic sedimentology and stratigraphy of Saskatchewan’s Viking Formation, Mannville Group and Bakken Formation.