http://www.dgsdallas.org/en/cev/431
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Chemostratigraphy uses major, minor and trace element geochemistr
y to characterize, subdivide, and correlate strata. Traditionally within P
ioneer&rsquo\;s South Texas Asset Team, chemostratigraphy has been used pr
imarily for geosteering horizontal wells (Eagle Ford &\; Austin Chalk)
&ndash\; either real time or post-drill to determine lateral placement wit
h respect to a known target zone. These correlations are referenced back t
o geochemical signatures observed in pilot well(s).
After a compr
ehensive review, other applications of this geochemical dataset have been
identified, most¬\; notably the ability to estimate Total Organic Carbo
n (TOC), paleoredox facies, and proxies for VClay in terms of carbonate-ri
ch and clay-prone facies. Certain redox-sensitive trace metals such as mol
ybdenum and nickel are concentrated in organic carbon-rich intervals of th
e 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 abundance
s, anoxic or oxic conditions may be inferred. This dataset was used to elu
cidate vertical and lateral paleoredox conditions and facies variability w
ithin the organic-rich Eagle Ford Shale and how that variability can affec
t 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 th
rough pre-stack seismic inversion were used to propagate the geochemical d
ata from wells into 3D volumes. This estimation of the geochemical respons
e 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&rsquo\;s &lsquo\;swe
et spot&rsquo\; acreage of DeWitt and Karnes counties. Well look backs in
these counties have consistently shown that TOC and VClay can be correlate
d to well performance. Estimated TOC and brittleness from inorganic geoche
mistry within horizontal wells and the extension of this geochemical data
to 3D via relationships with geomechanical properties from seismic inversi
on provide another tool to evaluate variability as well as high-grading in
tervals within the Eagle Ford Formation across Pioneer&rsquo\;s acreage po
sition.