A stratigraphic and sedimentologic analysis of a lower Atoka sandstone, frontal Ouachita thrustbelt, Western Arkansas

Journal Article · Fri Sep 01 04:00:00 EDT 1995 · AAPG Bulletin

OSTI ID:159954

Vader, D E ^[1]

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1. Univ. of Arkansas, Fayetteville, AR (United States)

Prolific lower Atoka (Pennsylvanian) gas reservoirs have been exploited in the frontal Ouachita thrustbelt of eastern Oklahoma. Although the thrustbelt extends into western Arkansas, Pennsylvanian reservoirs have not been recognized. A lower Atoka sandstone unit, exposed behind the Ti Valley thrust fault, exhibits characteristics that indicate favorable reservoir quality. Three zones are distinguished by grain size, mineral composition and sedimentary structures. The stratigraphically lowest zone is very fine grained and is composed mostly of monocrystalline quartz with a clay matrix. Sedimentary structures include scours, horizontal burrows and horizontal laminations. Porosity and permeability are nonexistent in this zone. Alternating sets of horizontally laminated fine to medium grained sandstones and bioclastic sandstone characterize the second zone. Secondary porosity has developed due to dissolution of skeletal grains. The stratigraphically highest zone exhibits porosity and permeability comparable to reservoirs within the Arkoma basin. Porosity values range from 6% to 24% with permeability as high as 248 millidarcies. The zone is a massively bedded, fine to medium grained sandstone. Monocrystalline and polycrystalline quartz are the dominant mineral components along with minor amounts of skeletal fragments. Porosity is secondary and has developed where pervasive chlorite grain coatings preclude silica cementation. The primary sedimentary structure is hummocky cross stratification implying deposition on a storm dominated shelf. The outcrop is significant in that it suggests: (1) the Arkoma {open_quotes}shelf{close_quotes} extended south of the present Ouachita thrustbelt trend and (2) reservoir quality rocks of Atokan age may be present in the subsurface behind the major thrust faults of the trend in western Arkansas.

• OSTI ID: 159954
• Report Number(s): CONF-951094--
• Journal Information: AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 9 Vol. 79; ISSN 0149-1423; ISSN AABUD2
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
ARKANSAS
CARBONIFEROUS PERIOD
EXPLORATION
GEOLOGIC FAULTS
PETROGRAPHY
PETROLEUM
RESERVOIR ROCK
SANDSTONES
STRATIGRAPHY