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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 77 (1993)

Issue: 1. (January)

First Page: 118

Last Page: 123

Title: Gamma-Ray Logging of Outcrops by a Truck-Mounted Sonde: GEOLOGIC NOTE

Author(s): Douglas W. Jordan (2), Roger M. Slatt (3), Robert H. Gillespie (2), Anthony E. D'Agostino (4), Charles G. Stone (5)


An Innovative Technique Has Been Developed to acquire gamma-ray logs from rock outcrops. A standard logging truck is driven to the top of a quarry or cliff, and a gamma-ray sonde is lowered down the face by cable to the base of the cliff. The sonde is then raised at a constant rate, and gamma-ray measurements are continuously recorded, a method similar to logging a borehole. The logging rate is slower than conventional (borehole) rates since, on a cliff face, the gamma-ray tool is exposed to less than half of the rock mass normally encountered in a borehole.

Outcrop logging of strata where the geometry and stratification character of the deposit is observed demonstrates the reliability and potential pitfalls in subsurface wireline log correlations and provides better visualization of interwell-scale lateral continuity (and discontinuity) of strata. These outcrop logs assist in developing an understanding of the properties of the strata responsible for a particular gamma-ray log response and demonstrate the necessary caution in interpreting vertical sequences, depositional environments, lateral continuity, and reservoir quality from gamma-ray logs.

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