Abstract: Influence of Diagenetic and Postlithification Processes on Porosity in Mississippian Carbonate Reservoirs of Southern Saskatchewan

Donald M. Kent, Kenneth L. Walters

The Mississippian Frobisher-Alida and Midale beds are the most prolific hydrocarbon-producing intervals in southeastern Saskatchewan. They account for 93.6% of the medium-gravity and 92.5% of the light-gravity crude production in that area. The hydrocarbon reservoirs in these units are composed of varied carbonate-rock microfacies and the reservoir quality of the microfacies has been either enhanced or reduced by diagenetic and postlithification alterations which have taken place during the eogenetic, mesogenetic, or telogenetic stages of burial.

The porosity has been enhanced primarily during the mesogenetic and telogenetic stages of dolomitization and selective dissolution of constituent particles and cementing minerals. The destruction of porosity appears to have begun in the eogenetic stage and to have continued into the telogenetic stage. Those processes recognized as having been active during each of the burial stages include: (1) eogenetic--submarine and phreatic cementation by calcium carbonate and evaporitic minerals, internal sedimentation, and silicification by both replacement and cavity-filling silica; (2) mesogenetic--precementation compaction; coarse sparry calcite cementation, and pressure solution; (3) telogenetic--precipitation of void-filling anhydrite, and replacement of calcium carbonate rocks by metasomat c anhydrite.

Anhydrite void filling is most common at the pre-Mesozoic unconformity and consequently is a significant factor in the entrapment of the hydrocarbons in many of the reservoirs. In general, it may be concluded that the telogenetic processes, both porosity enhancing and porosity reducing, are probably the most important reservoir developers.

AAPG Search and Discovery Article #90964©1978 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah