Abstract: Effects of Burial Stages on Porosity in Reservoir Rocks in Mississippian Strata of Southern Saskatchewan
D. M. Kent, K. L. Walters
Hydrocarbons are produced from several carbonate microfacies in the Mississippian strata of southern Saskatchewan. Porosity types in these microfacies appear to be the result of either the alteration of primary porosity or the evolution of secondary porosity during eogenetic, mesogenetic, or telogenetic stages of burial.
Eogenetic alterations are exemplified best by the deposits of vadose carbonate silt and meniscus and microstalactitic cements in several oolitic sandstone deposits. Mesogenetic changes, which are more common, include those that have resulted from either neomorphism or compaction. Both aggrading and degrading neomorphic processes are thought to have enhanced the porosity of some reservoir rocks, particularly in those microfacies that were originally micritic skeletal sandstones or calcite-cemented, particle-supported, skeletal sandstones. In either lithology, the enhancement appears to have resulted from the formation of voids at enfacial junctions due to interfering crystal growth or along poorly fitting boundaries between neomorphically formed grains. On the other hand precementation compaction has had a detrimental effect on the original porosity of particle-supported skeletal and nonskeletal sandstones because of grain-boundary solution which has caused a closer packing of the grains and reduced the size of the original interparticle voids.
The effects of telogenetic processes are common within a few tens of feet below the pre-Mesozoic unconformity. In this zone porosity is destroyed or reduced by anhydritization and silicification and enhanced by post-lithification solution, dolomitization, and fracturing. In general, these latter processes have enhanced significantly the porosity of most Mississippian reservoir rocks by improving void openings and developing intercrystalline porosity.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC