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Dleep-water Sheet and Channel-fill Sandstones in the Wildhorse Mountain Formation, Oklahoma, USA

By
R. M. Slatt
R. M. Slatt
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B. Omatsola
B. Omatsola
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Published:
January 01, 2008

Abstract

Gas from the Pennsylvania Jackfork Group is generally considered to be trapped in large structures and to be produced from associated fractures. In outcrop, fractures are well developed in brittle, quartz-cemented sandstones. However, some outcrops also reveal the presence of friable and poorly cemented sandstones, which if present in the subsurface, could also comprise good reservoirs. Identifying these two different reservoir types (fracture vs. matrix porosity) can be challenging in structurally complex areas where there are little or no seismic profiles and only conventional well logs. Outcrop studies have shown that the Wildhorse Mountain Formation of the Jackfork Group is mainly composed of deep-water sheet and channel-fill sandstones. Each of these classes has distinctive features that allow their differentiation from conventional core, dipmeter, or borehole image logs, and sometimes conventional well logs. Sheet sandstones tend to be interbedded with shale to give a relatively low net sand; beds are laterally continuous for long distances, and stratigraphic dips are uniform and of relatively low angle. channel-fill sandstones tend to be thick-bedded, with higher net sand, lenticular external geometry, and variable stratigraphic dips. These patterns are readily identified on borehole image and dipmeter logs. Outcrop and subsurface studies in eastern Oklahoma have indicated the sheet sandstones are highly quartz-cemented, moderately to well sorted, with little primary porosity. channel-fill sandstones are more poorly sorted, contain clay, and are moderately to poorly cemented. Porosity in the sheet sandstones tends to be fracture-dominant and that in the channel sandstones tends to be matrix-dominant. Using these outcrop and well log criteria, it is possible to differentiate these two different reservoir types in the subsurface.

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Contents

AAPG Studies in Geology

Atlas of Deep-Water Outcrops

Tor H. Nilsen
Tor H. Nilsen
Desceased
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Roger D. Shew
Roger D. Shew
University of North Carolina
Wilmington, North Carolina
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Gary S. Steffens
Gary S. Steffens
Shell International E&P
Houston, Texas
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Joseph R. J. Studlick
Joseph R. J. Studlick
Maersk Oil America Inc.
Houston, Texas
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American Association of Petroleum Geologists
Volume
56
ISBN electronic:
9781629810331
Publication date:
January 01, 2008

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