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The AAPG/Datapages Combined Publications Database

Rocky Mountain Association of Geologists

Abstract


Revisiting and Revitalizing the Niobrara in the Central Rockies, 2011
Pages 204-218

Chapter 13: Outcrop Gamma-Ray Logging Applied to Subsurface Petroleum Geology

Roger M. Slatt, James M. Borer, Brian W. Horn, Hisham A. Al-Siyabi, Sarah R. Pietraszek

Abstract

Developing a gamma-ray log profile of an outcrop with a hand-held scintillometer has many applications to subsurface petroleum geology. The outcrop gamma-ray log provides a readily understandable bridge between what is observed in outcrop and what is to be interpreted on well logs and seismic records. Several examples are presented in this paper that demonstrate major applications.

An outcrop from the Cretaceous Mesaverde Group in Colorado provides an excellent example of the use of outcrop gamma-ray logs to better visualize spatial variability of depositional settings for improved well log correlations. Outcrops from the Cretaceous Almond Formation, Niobrara Formation, and Graneros Shale in Colorado serve as examples of outcrop gamma-ray logging used to correlate outcrops with their subsurface equivalents for improved lithologic and stratigraphic interpretation of well logs. Outcrops of the Cretaceous Sharon Springs Member of the Pierre Shale in Colorado and the Eocene Green River Formation in Wyoming provide examples of the application of outcrop-gamma ray logging to identify and characterize organic-rich shales in outcrops and on well logs. Outcrops of the Pennsylvanian Jackfork Formation in Arkansas demonstrate the use of outcrop logging to yield improved interpretation of reservoir quality on well logs and for one- and two-dimensional seismic modeling. An outcrop of Precambrian and Cambro-Ordovician rocks from Algeria provides an example of outcrop logging to recognize unconformities and other major surfaces on well logs. An outcrop of the Niobrara Formation in Colorado is used as an example for improved understanding of horizontal gamma-ray log response.

The example logs presented are all derived with a hand-held scintillometer. This technique is simple, quick, and relatively inexpensive, so is recommended for any outcrop work that is intended to be applied to subsurface well logs or seismic interpretation.


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