SPWLA
Monthly Luncheon Meeting
Thursday – October 17, 2019
PanAm Building
601 Poydras St, Suite 1600
New Orleans, LA 70130
11:30 – 1:00 pm
$25
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Thermal maturity-adjusted log interpretation (TMALI) in organic shales
Presented By: Paul Craddock
Senior Research Scientist, Schlumberger-Doll Research
ABSTRACT
The
petrophysical interpretation of downhole logs requires knowledge of accurate
matrix properties. In organic-rich mudrocks (shale), the presence of abundant
kerogen (solid, insoluble organic matter) has a particularly large and variable
impact on matrix properties. Matrix properties are highly sensitive to kerogen
properties because kerogen is compositionally distinct from minerals that
comprise the remainder of the matrix. In practice, kerogen properties must be
accurately known to separate tool responses to kerogen (in the matrix volume)
and fluids (in the pore volume), to arrive at accurate volumetric
interpretations. Unfortunately, relevant petrophysical properties of kerogen
are nearly always unknown in the formation of interest, and otherwise
impractical or impossible to measure.
In this talk, I
will present the petrophysical properties of kerogen from the study of more
than 50 global shale samples. The determined kerogen properties include
measured chemical composition and absolute density, as well as calculated
nuclear properties such as apparent log density, hydrogen index, thermal and
epithermal neutron porosities, photoelectric factor, macroscopic capture
cross-section (Sigma), and fast neutron cross-section. For kerogen samples
relevant to the petroleum industry (predominantly type II with thermal maturity
ranging from immature to dry gas), it is found that petrophysical properties
are controlled mainly by thermal maturity, with differences between
basins/formations having relatively little effect on kerogen properties. As a
result, universal curves can be established that relate kerogen properties to
thermal maturity. This thermal maturity-adjusted log interpretation (TMALI) establishes
a consistent framework to evaluate organic shales globally, requiring only
knowledge of the thermal maturity of the play of interest, and provides more
accurate, robust, and confident estimates of critical formation parameters
including porosity, saturation, and hydrocarbon-in-place.
Paul Craddock is a geochemist and Senior
Research Scientist in the Applied Math & Data Analytics Department at
Schlumberger-Doll Research Center in Cambridge, Massachusetts. His research provides
solutions for reservoir characterization using nuclear, X-ray, and infrared
spectroscopy methods, such as to derive saturation in low-resistivity pay in
conventional reservoirs using nuclear spectroscopy; identify favorable pay for
well placement and production in unconventional resources (“RPI”); integrate
cuttings and logs for enhanced petrophysics in shale (“DRIFTS”); and optimize
kerogen endpoints for global shale interpretations (“TMALI”). Paul received a
PhD in chemical oceanography from Massachusetts Institute of Technology/Woods
Hole Oceanographic Institution in 2009 and has co-authored more than 40
technical journal and conference publications. Paul is twice a SPWLA
Distinguished Speaker and his paper “Thermal maturity-adjusted log interpretation
(TMALI) in organic shales” was awarded Best Oral Presentation at the 2019 SPWLA
60th Annual Logging Symposium.