Abstract

The Duperow is a substantial hydrocarbon-producing formation in the area. Included in the Billings Nose are the TR (Theodore Roosevelt), Big Stick, Whiskey Joe, Four Eyes, White Tail, Fairfield, Elkhorn Ranch, and Tree Top fields. Duperow rocks consist principally of dolomites, limestones, and anhydrites. Most of the dolomites appear to be of diagenetic origin although some primary dolomites do occur. Primary dolomites are parallel and wispy laminated mudstones, deposited principally as part of the supratidal facies in association with stromatolites. Secondary replacement dolomites occur throughout the section, but seem to selectively replace the matrix in the stromatoporoid zone of the shallow subtidal facies and intraclasts in the intertidal facies. Included in the supratidal facies are anhydrites. Anhydrites range in habit from the typical replacive nodules to the less common chickenwire and layered forms. Layered types appear to be associated with ephemeral hypersaline ponds in the supratidal. In general, porosity is poor in this facies. The intertidal facies consist of intraclastic wacke-packstone. Intraclasts and fragmented brachiopods and mollusks are the principal allochems. Bioturbation has destroyed most laminations. Apparent selective replacement of intraclasts constitute the majority of the porosity in this facies. The subtidal facies includes stromatoporid and bioturbated zones. Sparsely fossiliferous wackestones are the predominate fabric, but stromatoporid boundstones and coral, brachiopod packstones are common. Good intercrystalline porosity occurs in the matrix of the stromatoporid zone. End_of_Article - Last_Page 554------------

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