ABSTRACT

A case history of a textural and reservoir analysis of transgressive, reeffringed, limestone banks or platforms of the Upper Devonian Beaverhill Lake formation in the Swan Hills area of Alberta is presented to illustrate the relationships of grain, matrix and cement variants of carbonate rocks to porosity and permeability determinations. Successive rims of organic lattice, stromatoporoidal and algal, atoll-like "build-ups," with granular matrix, separate generally medium to dark brown pelleted lime muds containing abundant amphiporids, and intercalated lighter colored lagoonal carbonates, from open marine shales and nodular, argillaceous, crinoid- and brachiopod-rich limestones. The most effective reservoir material along the reef fronts or terraces consists of vuggy organic lattice, algal encrusted amphiporids (minor developments) and reworked stromatoporoidal, algal and amphiporid material with intra-organic vugs, embedded in a porous, well-sorted, micro to finely granular or pellet matrix. Matrix grain size studies are essential to exploration and secondary recovery problems, as the granular material grades laterally into chalky or micrograined limestones which were laid down under lower energy conditions. Matrix granularity ratio outlines are considered to be superior to ecological maps (percentage of algal and stromatoporoidal material) in the prediction of shoal areas. Slice maps and textural studies are utilized to demonstrate transgressive shoals and progressive submergence of the bank atolls of this area.