Facies, Fabrics, and Porosity of Selected Pre-Permian Rocks in Williston Basin, North Dakota: ABSTRACT

Abstract

Cores of pre-Permian rocks presented include most major carbonate depositional facies, fabrics, and porosity types, as well as a terrigenousclastic delta and barrier island complex. Stratigraphic units discussed span the Tippecanoe to Absaroka sequences. Formations and intervals included are the Tyler, Mission Canyon, Ratcliffe, Frobisher-Alida, Bakken, Birdbear, Duperow, Winnipegosis, Ashern, and Interlake. All of these units, except the Ashern Formation, have produced substantial amounts of hydrocarbons, and cores show different facies, fabrics, and porosity types associated with them. Facies and fabrics vary considerably both interformationally and intraformationally throughout the presented pre-Permian, sequences. Depositional facies represented in the rocks include subtidal, intertidal and supratidal deposits from both the marine and transitional marine (deltaic and barrier island) depositional environments. The most common carbonate lithofacies are mudstones, wackestones, and packstones, although boundstones and grainstones are also present. The most common terrigenous clastic lithofacies are shales, silty mudstones, and both mature and immature sandstones. Notable facies include evaporites (both shallow and deep water), stromatoporoids, ostracodal limestones, and thin coal beds. Significant sedimentary structures include burrows, flat pebble intraclasts, desicc tion cracks, birdseye structures, cone-in-cone structures, compaction slickensides, and collapse breccias. Porosity types common to all, except the Ashern, Bakken, and Tyler, are intercrystal, interparticle, moldic, vuggy, and breccia. Significant porosity in the Sanish, Ashern, and Bakken formations is from fractures, whereas in the Tyler, interparticle porosity dominates. End_of_Article - Last_Page 1331------------