The Sedimentology and diagenesis of the Cadomin formation, Elmworth area, northwest Alberta
The Cadanin Formation Blairrrore Group of is the basal unit of Northwestern Alberta. the Lower Cretaceous It is a wedge-shaped CC>njlaneratic molasse deposit of the Columbian Orogeny. Laramide thrusting and subsequent erosion exposed the thickest sections of Cadanin in the Foothills of the Rocky mountains. Beyond the eastern limit of OJerhrusti~ the deposit has been deeply buried in the Alberta Deep Basin. There it forms a thin, laterally extensive sheet-like unit which overlies a regional unconfirmity of low, topographic relief. The Cadanin was deposited in an alluvial-fan - braidplain environment. Climatic conditions were humid. Braided river systems have reworked the detritus lateraly and distally and a thin yet widespread distribution has resulted. Systematic textural variations and facies assemblages have been identified and a Scott to Donjek type braided-river deposit is inferred. Proximal to distal trends include decreasirg clast-size, increasing sand content, and a decreasing proportion of bimodal textures while poorly sorted textures are increasingly abundant. In the subsurface, the unit forms a gently southwest dipping monocline in which a Deep Basin type hydrocarbon reservoir has developed. Porous and permeable water-bear is strata pass downdip into poor reservoir quality gas-saturated strata. Significant gas reserves have been established in the Elmworth Area but production is lirnited to higher permeability zones. Permeability and ultimate reservoir potential is a function of the primary depositional textures and the diagenetic modifications. Moderately sorted and poorly sorted conglomerate textures generally have higher porosities and permeabilities than bimodal conglomerate textures of clast or matrix-supported pebbles and sand. A variation in diagenetic modification exists in the Cadornin because of a geothernal gradient and an increasing depth of burial towards the rou thrust of the Deep Basin Area. Permeabilities are reduced in zones of quartz overgrowth cementation and added authigenic clay matrix. Secondary porosity is developed and permeabilities enhanced in zones of disrolution and leaching by pore fluids. Successful exploitation of these conglomerates depends on knowledge of reservoir facies textures and diagenetic controls.
Bibliography: p. 131-137.
Varley, C. J. (1982). The Sedimentology and diagenesis of the Cadomin formation, Elmworth area, northwest Alberta (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/17848