ROBINSON, R.A.J., E.ADKINS, C.R.BATES, M. RODRIGUEZ-PLAZA, and A.R. PRAVE, Sedimentary Systems Research Group, University of St Andrews, St Andrews, KY16 9ST, Scotland

Abstract: Outcrop to Subsurface Gamma-Ray Log Integration: Extracting Quantitative Information on Geophysical Parameters from the Frontier Formation, Wind River Basin, USA

The Cenomanian-Turonian Frontier Formation of the Maverick Springs area,Wind River Basin, USA is a superbly exposed sequence of prograding shallow-marine to nonmarine sequences. The quality of exposures allows 3-D description of sandstone body geometry and, combined with regional mapping, subsurface wireline logs and 2-D and 3-D seismic, defines the width of the Frontier system and the changes in sandstone architecture in depositional strike and dip orientations. Outcrop gamma-ray profiles, generated by both a handheld scintillometer and a spectrometer, were analysed to quantify how the geophysical signatures relate to individual facies units and how both vary along the outcrop. The gamma-ray data have been compared to stratigraphic geochemical signatures and petrographic data to extract values of percentage sand, porosity and permeability. In addition, the rates of change of these parameters between closely spaced transects has been quantified and linked to the outcrop. Across the gas producing field, surface gamma-ray profiles and wireline well logs from more distal subsurface units are easily correlated. Production data is combined with the wireline signatures and compared to the outcrop statistical model. The observed outcrop rates of change of percentage sand, porosity and permeability for individual facies unit are applied to each well to provide statistically reasonable distributions of the parameters. The technique allows a predictive capability of assessing a reservoir?s potential and aids in designing the interwell drilling strategy.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England