Eagle Ford Sweet Spot Mapping
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 geosteering 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), paleoredox facies, and proxies for VClay in terms of carbonate-rich and clay-prone facies. Certain redox-sensitive trace metals such as molybdenum 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, Bee, DeWitt, Karnes, La Salle, Lavaca 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. This dataset was used to elucidate vertical and lateral paleoredox conditions and facies variability within the organic-rich Eagle Ford Shale and how that variability can affect well performance.
This geochemical dataset was integrated with geomechanical data to develop relationships for estimating the geochemical response from geomechanical properties, using multi-attribute transforms, neural network analysis, and principle component analysis. Based on these relationships, 3D volumes of specific geomechanical properties derived through pre-stack seismic inversion were used to propagate the geochemical data from wells into 3D volumes. This estimation of the geochemical response away from the wellbore using 3D surface seismic data provides a powerful means of improving the lateral resolution and predictive capabilities of the geochemical analysis.
TOC and the brittleness (VClay) of the Eagle Ford are two 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 and VClay can be correlated to well performance. Estimated TOC and brittleness from inorganic geochemistry within horizontal wells and the extension of this geochemical data to 3D via relationships with geomechanical properties from seismic inversion provide another tool to evaluate variability as well as high-grading intervals within the Eagle Ford Formation across Pioneer’s acreage position.