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Effective Application and Utilization of Inorganic Geochemical Data in Shale Resource Plays: A Case Study from the Appalachian Basin

Martinez-Kulikowski, Nahysa; Wright, Milly; Reynolds, Andrea

Shale resource plays are becoming increasingly important within the petroleum industry both in the U.S. and globally. However, understanding how shales change both temporally and spatially with respect to mineralogy and depositional environment, and assessing how these changes may relate to reservoir quality are not well understood. In recent years, inorganic elemental analyses have been routinely applied to many shale plays to better understand mineralogy, stratigraphy and depositional environment, with this approach being particularly effective within Eagle Ford and Haynesville formations. In this study, results are presented from inorganic elemental analyses from a series of Appalachian shales including Marcellus and Burket sequences in order to explore if this approach can provide useful insights in a relatively carbonate-poor shale system.

Data for up to 50 elements have been acquired from core and cutting samples from wells drilled in Tioga Co., Pennsylvania. The results of these analyses are discussed in conjunction with stratigraphic data, TOC and XRD analyses to provide an integrated stratigraphy and characterization of these sections.

Several elements and elemental ratios such as Ca/Al, Th/U, K/Rb, Na/Al, Zr/Al, Al/bases and U show significant vertical changes through the study intervals. They allow each sequence to be subdivided into several broad-scale chemostratigraphic packages and higher resolution units that are correlated to produce a robust chemostratigraphic correlation framework within this area. Furthermore, these ratios provide helpful insights into various processes, since they reflect lithological changes (Ca/Al), grain size (Zr/Al), potential provenance change (Na/Al and K/Rb), and variations in environmental conditions (U, Al/bases).

In addition to classic chemostratigraphy, this study also demonstrates how inorganic whole rock geochemical data can be used to determine paleoredox facies, model mineralogy and TOC contents, and be used to estimate biogenic silica contents.

Paleoredox conditions play an important role in determining organic matter preservation and consideration of redox-sensitive elements, such as V, Ni, Th, U, and Mo provides a means to determine the degree of anoxia during deposition. Major element concentrations can be used to model most mineral phases, and by incorporating select trace elements, typically U and Ni, TOC content can also be modeled. These models are compared to XRD and measured TOC values to demonstrate the efficacy of this methodology.

Although it is appreciated that all shale plays have different characteristics, the applications of inorganic elemental data outlined in this study are readily exportable to any shale resource play. Information generated from this type of dataset may be tailored to a number of different uses from regional correlations to aiding in lateral well completions.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013