--> ABSTRACT: Petrology and Hydrocarbon Reservoir Potential of Mississippian (Chesterian) Sandstones, Black Warrior Basin, Mississippi, by Steve B. Hughes and Maurice A. Meylan; #91036 (2010)

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Petrology and Hydrocarbon Reservoir Potential of Mississippian (Chesterian) Sandstones, Black Warrior Basin, Mississippi

Steve B. Hughes, Maurice A. Meylan

The character and reservoir quality of six different Mississippian (Chesterian) sandstone units in frontier areas of the Black Warrior basin of Mississippi have been determined by core inspection, thin-section examination, and x-ray diffractometry. A total of 113 samples from ten wells was taken from cores of the following sandstones: the Lewis, a calcareous sandstone at the top of or just above the Lewis that we refer to as the Lewis limestone, the Evans, the Rea, the Sanders, and the Carter. Hydrocarbon production from the basin, which is located in northeastern Mississippi and northwestern Alabama, is mostly shallow gas (with minor gas condensate and oil) from these units. Sample depths range from about 2,500 ft (762 m) in northern Chickasaw County to about 5,500 ft (1 676 m) in Monroe and Lowndes Counties, with the deepest samples coming from almost 11,000 ft (3,353 m) in northern Clay County.

The sandstones are very fine to fine-grained quartzarenites having framework grains that average 98.3% monocrystalline quartz, 0.8% polycrystalline quartz, 0.2% feldspar, 0.1% metamorphic rock fragments, 0.3% sedimentary rock fragments, and 0.2% muscovite. Remnant clay rims under secondary overgrowths generally outline subrounded to well-rounded grains. Little variation occurs in the character of the framework grains between the different sandstone units.

Differences in degree of compaction and the percentage and type of cement lend some individuality to the sandstones, however. The most common cement is silica precipitated as secondary overgrowths on detrital quartz. Less common is a carbonate (dominantly dolomite with some calcite) cement, but in one highly oolitic Lewis limestone sample, 54.8% is carbonate. In many samples, the carbonate cement has corroded adjacent framework grains. Authigenic clays, primarily kaolinite, and pyrite occur as postframework grain dissolution cements.

Except where cemented by carbonate, the sandstones are highly compacted, as is indicated by sutured, concavo-convex, and long grain contacts as well as occasional microstylolites. Macroscopic inspection of cores revealed numerous stylolites in four wells, including all three producing wells sampled. Petrographic porosity ranges from 0.0 to 9.3%, averaging 1.6%. Most porosity is secondary, resulting from the dissolution of carbonate and silica cement, and possibly some of the few original unstable framework grains. The Lewis sandstone, at a depth of about 11,000 ft (3,353 m), has no porosity, all pore space being occluded by pyrite.

Relative percentages of framework grains indicate that the provenance terrane was most likely a stable craton interior, presumably to the north, having a sedimentary rock cover with very mature quartz sandstones as a major component. This composition is in contrast to the overlying Pottsville (Pennsylvanian) rocks of the Black Warrior basin, which contain 10-18% metamorphic rock fragments, and which probably represent detritus shed from a rising Ouachita terrane to the south and southwest. Based on the very fine-grained nature of the sand and the presence of marine fossils, oolites, and thin shale interbeds, the Chesterian sandstones were most likely deposited offshore from deltas recognized to the north and east of the study area.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.