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Subsurface to Outcrop: Linking Rock Physics and Depositional Environment to Seismic Reflectivity Data, Kaiparowits Plateau, Utah

Karenth l. Dworsky, Cari L. Johnson, Lisa Stright, and Tiziana Vanorio
University of Utah

The Cretaceous John Henry Member provides excellent outcrop exposures of fluvial, paralic, and marine stratigraphy across the Kaiparowits Plateau in southern Utah. Previous outcrop studies link fluvial deposits in the east to shoreline facies in the west. There have only been a handful of studies of the transitional facies in the center of the plateau; the purpose of this study is to begin to address this data gap by synthesizing a newly acquired 2-D seismic line with available core from a nearby borehole (< 100 m from seismic line). To make a more accurate interpretation of seismic reflection data, an understanding of the elastic rock properties of each facies is required. Grain and bulk density, P- and S- wave velocity, Helium porosity and Klinkenberg-corrected permeability were acquired from 60 core plugs. The plugs statistically represent 9 different marginal marine and fluvial facies. Thin-sections from 15 samples and QEMSCAN analysis were used to obtain mineralogy and clay content. The results from core plug measurements demonstrate variability between the mudstone and shale facies, and the sandstone-dominant facies. Porosity and velocity values from the mudstone and shale facies have small ranges (7-13%; 1950-3985 m/s); whereas the sandstone facies are more dispersed (9-37%; 1400-4230 m/s). The permeability of mudstone and shale facies was too low to measure (< 1 mD); conversely, the sandstone facies had considerable permeability ranges (1-1140 mD). Clay content, clay type and organization, as well as variations in mineralogy are indicators of scatter in the velocity, porosity and permeability values of the sandstone facies. These rock physics analyses used in conjunction with identified depositional environments from the core enable a more accurate interpretation of the acquired seismic data.

AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013