--> Abstract: Utilization and Requirements for Outcrop Gamma-Ray Logging, Arkoma Basin Turbidite and Tidal Examples, by Roderick Tillman; #90039 (2005)

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Utilization and Requirements for Outcrop Gamma-Ray Logging, Arkoma Basin Turbidite and Tidal Examples

Roderick Tillman
Consulting Geologist, Tulsa, OK

Results from recent highway roadcut analysis in NW Arkansas are examples of utilization of outcrop gamma-ray logs to aid in recognizing tidal and estuarine influences in nearby reservoirs previously considered to be deltaic. Tidal point bars, tidal flats and tidally influenced fluvial sandstones were correlated from the surface to nearby fault-separated wells and outcrops. 360' Jackfork turbidite sandstones also outcrop.

There are numerous advantages from incorporating outcrop gamma-ray logs with other nearby subsurface and surface data. 1. Allows correlation of outcropping sandstones with: (a) well logs and outcrops in adjacent fault blocks (b) with cores in nearby wells 2. Allows identification of environments of deposition in nearby wells. 3. Where subsurface names have taken historical precedence allows outcrops to be identified using subsurface names. 4. Helps in identifying breaks in outcrop stratigraphy which were not obvious without outcrop gamma-ray logs.

Requirements for quality gamma-ray log surveys: 1. Total gamma-ray logs taken at 0.5 ft spacing (1 ft in shales) using average of three readings. 2. Minimum of three persons required for efficient survey 3. Careful measuring, marking of rocks and interpretation of measured sections. 4. GR survey over exact measured section locations. 5. Ability to carefully correlate laterally for short distances in order to obtain greater vertical interval for logging. 6. Patience

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005