Dleep-water Sheet and Channel-fill Sandstones in the Wildhorse Mountain Formation, Oklahoma, USA
R. M. Slatt, B. Omatsola, 2008. "Dleep-water Sheet and Channel-fill Sandstones in the Wildhorse Mountain Formation, Oklahoma, USA", Atlas of Deep-Water Outcrops, Tor H. Nilsen, Roger D. Shew, Gary S. Steffens, Joseph R. J. Studlick
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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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Tor H. Nilsen, a red-haired Scandinavian who stood more than six feet tall, died October 9, 2005, at his San Carlos, California, home. This was after a valiant five-year fight with melanoma cancer. He was 63. His ashes were scattered at his family plot in Norway in 2006.
He was born in New York City on November 29, 1941, to Mollie Abrahamson and Nils Marius Nilsen of Mandal, Norway, and was the first of their children to be born in the United States. After graduating from Brooklyn Tech, he earned his B.S. in geology from City College of New York in 1962. While there, his prowess on the basketball court impressed a scout from the New York Knicks, but Tor went on to graduate school and earned his M.S. and Ph.D. degrees in geology from the University of Wisconsin at Madison in 1964 and 1967, respectively. His M.S. thesis was a study of Precambrian metasedimentary deposits in the Lake Superior area, and his Ph.D. thesis was a study of Devonian alluvial-fan deposits of the Old Red Sandstone in western Norway.
Dr. Nilsen’s principal expertise was in depositional systems analysis, stratigraphic analysis, and the relationships among tectonics, eustasy, and sedimentation. He began his industry career in 1967 as a research geologist with the Shell Development Company in Houston, Texas, and Ventura, California, where he worked on the tectonics and sedimentation of Tertiary shelf systems of coastal California. He subsequently spent two years with the U.S. Army Corps of Engineers as the Military