Paleokarst Reservoirs in the Lower Carboniferous (Mississippian) Madison Group and the Jura-Cretaceous Success Formation of West-Central Saskatchewan
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 seven 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, 4) mudstone, 5) chaotic mud and chert rubble breccia/conglomerate, 6) crackle-mosaic breccia, and 7) matrix-supported chaotic breccia. The karst facies associations represented are; 1) collapsed cave, 2) preserved cave roof, 3) epikarst, and 4) soil breccia. 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. This research has solidified the interpretation of the Madison Group’s and Success Formation’s relationship as a paleokarst terrain as well as demonstrate a predictive model for further hydrocarbon exploration within and outside of the study area.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019