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Abstract

AAPG Bulletin, V. 91, No. 2 (February 2007), P. 191-214.

Copyright copy2007. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/08310605114

Three-dimensional facies architecture and three-dimensional calcite concretion distributions in a tide-influenced delta front, Wall Creek Member, Frontier Formation, Wyoming

Keumsuk Lee,1 M. Royhan Gani,2 George A. McMechan,3 Janok P. Bhattacharya,4 Stephanie L. Nyman,5 Xiaoxian Zeng6

1Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78713-8924; [email protected]
2Energy and Geoscience Institute, University of Utah, 423 Wakara Way, Suite 300, Salt Lake City, Utah 84108; [email protected]
3Center for Lithospheric Studies, University of Texas at Dallas, P.O. Box 830688, Richardson, Texas 75083-0688; [email protected]
4Geosciences Department, SR1 Rm. 312, University of Houston 4800 Calhoun Rd., Houston, Texas 77204-5007; [email protected]
5Department of Earth and Ocean Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand; [email protected]
6Center for Lithospheric Studies, University of Texas at Dallas, P.O. Box 830688, Richardson, Texas 75083-0688; [email protected]

ABSTRACT

Ground-penetrating radar (GPR) has been used to image the three-dimensional (3-D) internal structure (and, thus, the 3-D facies architecture) of a top-truncated delta front in the topmost parasequence in the Wall Creek Sandstone Member of the Frontier Formation in Wyoming and to estimate the distribution of low-permeability concretions throughout the 3-D GPR volume.

The interpretation of the 3-D GPR data is based both on correlations with outcrop and on calibration with core data from holes within the survey grid. Two main radar facies (RF) are identified. Radar facies 1 corresponds to tide-influenced mouth bars formed by a unidirectional flow during delta progradation or bidirectional flow during tides, whereas RF2 is correlated with laterally migrating channels developed on previous bar deposits. The delta-front foreset beds dip in the same direction as the dominant paleocurrent indicators. The GPR interpretation is consistent with the outcrop interpretation that, following a regressive period, bars and channels were developed at the Raptor Ridge site before subsequent transgressive ravinement. The individual 3-D deltaic facies architectures were reconstructed from the 3-D GPR volume and indicate that the depositional units are larger than the survey grid.

Cluster analysis of the GPR attributes (instantaneous amplitudes and wave numbers) calibrated with the cores and the outcrop was used to predict the distribution of near-zero permeability concretions throughout the 3-D GPR volume; clusters of predictive attributes were defined and applied separately in the bars and channels. The predicted concretions in the bars and the channels are 14.7 and 10.2% by volume, respectively, which is consistent with those observed in the cores (14.7 and 10.5%, respectively), and their shape and thickness are also generally in consonance with those in the outcrop and cores. The estimated concretions are distributed in an aggregate pattern with irregularly shaped branches within the 3-D GPR volume, indicating that the cementation does not follow a traditional center-to-margin pattern. The concretions and 3-D geological solid model provide cemented flow baffles and a 3-D structural framework for 3-D reservoir modeling, respectively.

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