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Abstract

AAPG Bulletin, V. 93, No. 10 (October 2009), P. 1379-1401.

Copyright ©2009. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/06240908173

Sandstone-body dimensions in a lower coastal-plain depositional setting: Lower Williams Fork Formation, Coal Canyon, Piceance Basin, Colorado

Matthew J. Pranter,1 Rex D. Cole,2 Henrikus Panjaitan,3 Nicholas K. Sommer4

1Department of Geological Sciences and Energy and Minerals Applied Research Center, University of Colorado, UCB 399, Boulder, Colorado 80309; [email protected]
2Department of Physical and Environmental Sciences, Mesa State College, 1100 North Avenue, Grand Junction, Colorado 81501; [email protected]
3Colorado School of Mines, Golden, Colorado; present address: Heavy Oil Operating Unit, Chevron Pacific Indonesia, Duri 28884, Indonesia; [email protected]
4University of Colorado, Boulder, Colorado; present address: EnCana Oil and Gas (U.S.A.) Inc., 370 17th Street, Suite 1700, Denver, Colorado 80202; [email protected]

ABSTRACT

This study addresses the field-scale architecture and dimensions of fluvial deposits of the lower Williams Fork Formation through analysis of outcrops in Coal Canyon, Piceance Basin, Colorado. The lower Williams Fork Formation primarily consists of mud rock with numerous isolated, lenticular to channel-form sandstone bodies that were deposited by meandering river systems within a coastal-plain setting. Field descriptions, global positioning system traverses, and a combination of high-resolution aerial light detection and ranging data, digital orthophotography, and ground-based photomosaics were used to map and document the abundance, stratigraphic position, and dimensions of single-story and multistory channel bodies and crevasse splays.

The mean thickness and apparent width of the 688 measured sandstone bodies are 12.1 ft (3.7 m) and 364.9 ft (111.2 m), respectively. Single-story sandstone bodies (N = 116) range in thickness from 3.9 to 29.9 ft (1.2 to 9.1 m) and from 44.1 to 1699.8 ft (13.4 to 518.1 m) in apparent width. Multistory sandstone bodies (N = 273) range in thickness from 5.0 to 47.1 ft (1.5 to 14.4 m) and from 53.2 to 2791.1 ft (16.2 to 850.7 m) in apparent width. Crevasse splays (N = 279) range in thickness from 0.5 to 15.0 ft (0.2 to 4.6 m) and from 40.1 to 843.3 ft (12.2 to 257.0 m) in apparent width.

These data show that most sandstone bodies are smaller than the distance between wells at 10-ac spacing (660 ft [201 m]). Analyses of interwell sandstone-body connectivity suggest that even at 10-ac spacing, only half of the sandstone bodies are intersected and few are intersected by more than one well.

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