Petrology and Diagenesis of Deep-Water Sandstones, Ouachita Mountains, Arkansas and Oklahoma
Robert C. Morris, Kenneth E. Proctor, Michael R. Koch, 1979. "Petrology and Diagenesis of Deep-Water Sandstones, Ouachita Mountains, Arkansas and Oklahoma", Aspects of Diagenesis, Peter A. Scholle, Paul R. Schluger
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The Stanley and Jackfork Groups of the Ouachita Mountains consist of 18,000 feet of interbedded sandstones and shales deposited during the Late Mississippian and Early Pennsylvanian. Interest in their hydrocarbon potential has led to study of textures, compositions, and diagenetic alterations of these sandstones. The data and conclusions presented in this study are based on petrographic examination and porosity and permeability measurements of 187 samples collected from outcrop.
The Stanley sandstones are generally poorly sorted, very fine-grained feldspathio- and quartz wackes. They average 8% feldspar, 14% matrix, and 5% silica cement. Porosities range from 0.5-26% and permeabilities from 0.05-23 md.
Jackfork sandstones are predominantly moderately to poorly sorted, fine- to very fine-grained quartz arenites. They contain an average of 2% feldspar, 5% matrix, and 9% quartz cement. Porosities range from 0.5-14% and permeabilities from 0.05-9 md.
Pressure solution, silica cementation, and replacement of plagioclase by calcite have acted to reduce reservoir potential in both units, whereas corrosion and dissolution of framework grains have added secondary porosity. The presence of halloysite and kaolinite characterizes sandstones affected by surface leaching. Well sorted quartz arenites have poor reservoir quality as a result of extensive silica cementation. Characteristics associated with the retention or secondary development of reservoir potential include poor sorting, small mean grain sizes, and high matrix content.
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There are a number of gaping holes in accumulated knowledge within the discipline of sedimentology. Perhaps one of the largest holes has been the general subject of diagenesis in clastic rocks. It was therefore fortuitous that two symposia covering various aspects of diagenesis (mainly in clastics) were presented a year apart in different parts of the country but with the same motivation – to contribute to the closing of that knowledge gap. Sedimentologists now have a fairly good idea of the what and the how of sediment deposition. What happens after the sediments are lithified has frequently been ignored. It was the aim of both editors of this publication to approach the subject from two different viewpoints. Schluger directed a symposium which looked mainly at clastic reservoirs, and Scholle presented a symposium which examined various aspects of paleotemperature control of diagenesis.