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Regional Mapping of Genetic Units in the Almond Formation, Greater Wamsutter Field, Southwest Wyoming: Phase I: A Visual Twist from Old Approach: the Middle Main Almond Unit*

Natasha M. Rigg¹, Benjamin J. Kessel¹, James R. Lawrence², Will D. Monn¹, Fiona E. Kilbride¹, Brent W. Greenhalgh³, Robert J. Heckman², Alan J. Scott¹, and Mark L. Bacon¹

Search and Discovery Article #50157 (2009)

Posted January 30, 2009

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, TX, April 20-23, 2008. See companion articles, Search and Discovery Article #50158 (2009): Phase II: What to Do without a Flooding Surface: Mapping the Coastal Plain, and Search and Discovery Article #50159 (2009): Phase III: An Iterative Geostatistical Approach to High-grading Well Locations.

¹ Anadarko Petroleum Corporation, Denver, CO ([email protected])

² Marathon Oil Company, Houston, TX ([email protected])

³ Wexpro, Salt Lake City, UT ([email protected])

Abstract

The Almond Formation is a tight gas sand reservoir in the Washakie Basin. Currently, Wamsutter field is developed as a statistical play with poor correlation to geologic parameters. However, continued economic development requires an improved geologic model and better prediction of reservoir quality sands. We used a pragmatic approach to conduct a basin-wide, lithostratigraphic analysis of the Almond Formation within the Washakie Basin, using previous studies, increased well control, additional Almond core, and a unique cross-section display. Color-filled conductivity, gamma ray, and bulk density logs were plotted on a single track for each well. Cross-section lines were generated on a closely spaced grid, creating a “pseudoseismic” display, which illuminated flooding surfaces, sands, and coals. Using a Galloway-type approach to genetic stratigraphy, marine flooding surfaces in the middle Main Almond unit were correlated during Phase I of this project. By flattening on successive flooding surfaces and mapping of genetic intervals, several observations were made: 1) coarsening upward packages bounded by flooding surfaces were recognized regionally in the eastern part of the Washakie Basin and were interpreted as shoreface and deltaic complexes, 2) sub-seismic, syndepositional dip-slip, and post-depositional oblique-slip fault candidates were inferred in some areas of the field, and 3) genetic intervals can be used in further geostatistical modeling of the reservoir. Mapping genetic intervals bounded by regional flooding surfaces has improved our geologic model, allowed for better prediction of reservoir quality sand, and provided a framework within which further reservoir modeling can occur. This cost-effective approach shows that improving field economics with pragmatic geologic methods is viable even in a statistical play, and can be applied to other mature fields.