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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 68 (1984)

Issue: 6. (June)

First Page: 753

Last Page: 764

Title: Regional Variations of Previous HitPorosityNext Hit and Cement: St. Peter and Mount Simon Sandstones in Illinois Basin

Author(s): John Daniel Hoholick (2), Thomas Metarko (3), Paul Edwin Potter (4)

Article Type: Meeting abstract

Abstract:

Petrographic study of over 230 thin sections of cuttings, cores, and outcrop samples from the Ordovician St. Peter and Cambrian Mount Simon Sandstones of the craton-center Illinois basin yielded a series of maps that show a fairly regular distribution of primary and secondary Previous HitporosityNext Hit and cements.

Both primary and secondary Previous HitporosityNext Hit are present in the St. Peter Previous HitSandstoneNext Hit. Primary Previous HitporosityNext Hit is dominant from outcrop to 4,000 ft (1,219 m), whereas secondary Previous HitporosityNext Hit is dominant at depths greater than 4,000 ft. The overall Previous HitporosityNext Hit decline with burial is best described by an exponential equation: ^phgr = 30.8 exp (-0.00032 d), where ^phgr equals Previous HitporosityNext Hit and d is depth in feet. However, two linear equations provide the best fit of primary (above 4,000 ft, 1,219 m) and secondary Previous HitporosityNext Hit (below 4,000 ft). The chronology of Previous HitporosityNext Hit development appears to be closely related to the models proposed by P. J. C. Nagtegaal and includes early cementation, leaching of cement and framework, stabilized framework, and framework collapse.

Cements in the St. Peter are depth-dependent. They define distinct regions, are mappable, and include calcite, dolomite, silica overgrowths, chert, and chalcedony.

Virtually everywhere in the Mount Simon Previous HitSandstoneNext Hit, Previous HitporosityNext Hit is secondary and results from dissolution of authigenic and replacement cements, framework grains, and fractures. In the subsurface, Previous HitporosityNext Hit reaches a maximum of 18% at 5,000 ft (1,524 m) and drops rather sharply to 8% below 5,000 ft. As with the St. Peter Previous HitSandstoneNext Hit, the overall decline is best described by an exponential equation of the form: ^phgr = 31.08 exp (-0.00026 d).

Cements in the Mount Simon include quartz and feldspar overgrowths, hematite and kaolinite, carbonate, chlorite, and microquartz (chert). Basinwide maps show that they have a fairly regular distribution pattern in the basin.

We suggest that in the future, basinwide maps of cement and Previous HitporosityNext Hit types will be abundant. Such maps should enhance understanding of diagenesis, especially where map pattern can be related to fluid and burial history. Maps of cements and Previous HitporosityTop types can also aid the calibration of wireline logs, help find diagenetic traps, and help the design of drilling fluid systems and well-completion procedures. The routine use of cuttings rather than cores will hasten the advent of such maps.

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