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Expanding the Application of Chemostratigraphy within Cretaceous Mudrocks: Estimating Total Organic Carbon and Paleoredox Facies using Major, Minor and Trace Element Geochemistry

Beau Tinnin¹, Gemma Hildred², and Nahysa Martinez²
¹Pioneer Natural Resources, 5205 N. O’Connor Blvd., Suite 200, Irving, TX 75039
²Chemostrat Inc., 750 Bering Dr., Suite 550, Houston, TX 77057

Chemostratigraphy uses major, minor and trace element geochemistry to characterize, subdivide and correlate strata. Traditionally within Pioneer’s South Texas Asset Team, chemostratigraphy has been used primarily for geo-steering horizontal wells (Eagle Ford & Austin Chalk) – either real time, or post-drill to determine lateral placement, with respect to a known target zone. These correlations are referenced back to geochemical signatures observed in pilot well(s).

After a comprehensive review, other applications of this geochemical dataset have been identified, most notably the ability to estimate Total Organic Carbon (TOC) and paleoredox facies. Certain redox-sensitive trace metals, such as copper and nickel, are concentrated in organic, carbon-rich intervals of the Eagle Ford Formation. Using these trace metals, an estimation of TOC has been derived for certain key wells from Atascosa, DeWitt, Karnes and Live Oak counties. In addition, using the enrichment or depletion of minor and trace elements relative to their crustal abundances, anoxic or oxic conditions may be inferred. These data, especially when incorporated with biostratigraphy, result in a greater understanding of the depositional setting of the Gulf Coast Basin during the Cretaceous.

TOC is one of the key performance drivers in Pioneer’s ‘sweet spot’ acreage of DeWitt and Karnes counties. Well look backs in these counties have consistently shown that TOC can be correlated to well performance. Modeled TOC from inorganic geochemistry within horizontal wells will be another tool to evaluate the variability as well as high-grading intervals within the Eagle Ford Formation across Pioneer’s acreage position.


AAPG Search and Discovery Article #90164©2013 AAPG Southwest Section Meeting, Fredericksburg, Texas, April 6-10, 2013