An Oil-Producing Stromatoporoid Patch Reef in the Famennian (Devonian) Wabamun Formation, Normandville Field, Alberta

Abstract

The Normandville oilfield in the Peace River district of northcentral Alberta produces oil and gas from a stromatoporoid patch reef about 70 m below the top of the Wabamun Formation. Fracturing of the limestone associated with a set of northwestsoutheast striking faults has increased the porosity of the reservoir. The patch reef and its associated facies constitute the Normandville zone. The reef is 1.5 km2 in area and 10 m thick. The following lithofacies are distinguished in the zone: 1) the platform facies of nodular limestone that overlies and underlies the reef 2) the reef facies of stromatoporoid framestone and boundstone with minor rudstone, floatstone, and grainstone, 3) the reef-margin facies of stromatoporoid floatstone and rudstone with minor brachiopod and crinoid wackestone and packstone, 4) the cap facies of peloidal and skeletal grainstone, and 5) the off-reeffacies of peloidal and skeletal wackestones and packstones. The stromatoporoid fauna of five species is dominated by two species, one of Labechia and the other of Stylostroma. Stromatoporoids were reduced in numbers and diversity at the Frasniani Famennian extinction event but retained the ability to make reefs. Famennian faunas contain remnants of Frasnian genera and are marked by the resurgence of the order Labechiida. We review the world distribution of Famennian and Strunian stromatoporoids and revise generic assignments of many species. On a global scale, we find the faunas divided into three assemblages: 1) labechiids characterized by Stylostroma, 2) mixed labechiids and clathrodictyids with species of Atelodictyon, and 3) clathrodictyids without labechiids. The third assemblage is confined to western Europe and Kazakhstan in areas of the late Devonian Paleotethys ocean.