Upper Devonian Reef Oil Field--Redwater, Alberta, Canada: ABSTRACT

Abstract

The Redwater oil field discovered in 1948 has inplace reserves of 1,300 million bbl, about 64 percent of which will be recovered. The field is a single pool 58 sq mi in area along the updip edge of a large Late Devonian (Frasnian) limestone reef complex. The complex is more than 800 ft thick, roughly triangular in plan and about 225 sq mi in area. More than 900 wells have been drilled in the field area where normal forereef, reef, and backreef facies are recognized. Porosity and permeability were influenced by diagenesis, but conform with the primary facies patterns. The Redwater reef grew during a major subcycle within the Kaskaskian sequence. Transgression over shoal carbonate of the previous subcycle created a End_Page 529------------------------------ reef-prone shelf of moderate depth. The reef was enveloped by clayey and carbonate muds which prograded across the shelf. Nearly 3,000 million bbl of recoverable oil in Redwater and nine companion reefs attests to favorable trap-to-source relations in this basin setting. Recognition of reef-prone cycles of deposition and early understanding of the depositional/tectonic framework which affects reef distribution are important in guiding exploration for Redwater-like reefs in new areas. Local, less predictable factors can influence the effectiveness of the reefs as traps and the success of exploration. Subsequent basin history is critical, for depth of burial affects the feasibility of seismic exploration and imposes regional eometamorphic patterns of hydrocarbon distribution. End_of_Article - Last_Page 530------------