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AAPG Bulletin

Abstract

AAPG Bulletin, V. 99, No. 10 (October 2015), PP. 19291956

Copyright copy2015. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/05071514025

Stratigraphic architecture of fluvial deposits from borehole images, spectral-gamma-ray response, and outcrop analogs, Piceance Basin, Colorado

Gabriela I. Keeton,1 Matthew J. Pranter,2 Rex D. Cole,3 and Edmund R. (Gus) Gustason4

1Department of Geological Sciences, University of Colorado, 2200 Colorado Avenue, Boulder, Colorado 80309; present address: Anadarko Petroleum Corporation, 1099 18th Street, Suite 1800, Denver, Colorado 80202; [email protected]; [email protected]
2ConocoPhillips School of Geology and Geophysics, University of Oklahoma, 710 Sarkeys Energy Center, 100 East Boyd Street, Norman, Oklahoma 73019; [email protected]
3Department of Physical and Environmental Sciences, Colorado Mesa University, Grand Junction, Colorado 81501; [email protected]
4Enerplus Resources, 950 17th Street, Suite 2200, Denver, Colorado 80202; [email protected]

ABSTRACT

Lithofacies, architectural-element abundance, and estimates of dune-bedform height and channel sinuosity from borehole images (BHIs) and well-exposed outcrops allow for an expanded interpretation of the fluvial stratigraphic architecture of the Upper Cretaceous Williams Fork Formation. Sedimentologic and stratigraphic data from outcrops and detailed core descriptions of the Williams Fork Formation, Piceance Basin, Colorado, were used to compare attributes of fluvial architectural elements to BHI characteristics and spectral-gamma-ray (SGR) log motifs. Results show a distinct set of criteria based on BHIs that aid in the interpretation of lithofacies and fluvial reservoir architecture. In contrast, a practical correlation does not exist between outcrop- and core-derived SGR log motifs or thorium and potassium abundances and fluvial lithofacies or architectural elements.

Four electrofacies based on BHI characteristics (e.g., dip type, dip pattern, and color scheme) represent the most common fluvial lithofacies and are identified through comparison of paired, calibrated BHIs and core. Cross-bed-set thickness values from BHIs are used to calculate dune height as a proxy for flow energy. The lower and middle Williams Fork Formation represent low-energy meandering and higher energy braided systems, respectively, as evident by changes in channel sinuosity and architectural-element type. The upper Williams Fork Formation is divided into two intervals based on lithofacies, architectural elements, channel sinuosity, and net-to-gross ratio. The subdivision for the upper Williams Fork Formation represents a change from a lower energy, meandering fluvial system to a higher energy, lower sinuosity braided system as related to changes in accommodation through time.

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