This study aims to (1) correlate changes in chemical composition between 13C NMR and Rock-Eval pyrolysis and (2) investigate using both techniques for source rock evaluation. Rock-Eval measurements of S2 and HI correlated with aromatic and aliphatic carbon fractions from 13C NMR in determining generative potential and thermal maturity. Aromaticity from 13C NMR strongly correlated with HI from Rock-Eval as a parameter for assessing thermal maturity. Aliphatics from 13C NMR strongly correlated with potential hydrocarbons released, as measured by S2 from Rock-Eval. Combining 13C NMR and Rock-Eval provides data on kerogen structure, organic matter type, quality, and oil yields.

1. Assessing the Source Rock Potential Using Solid-
State 13C NMR Organic Geochemical Approaches
Charlie Keracik, Dr. William Hockaday, Dr. Steve Driese
Baylor University, Department of Geology, Waco, TX, 76706 USA
Introduction Methods
Results & Discussion
Conclusions & Future Work References
Acknowledgements
With high attention being focused towards the development of unconventional
fuels, the United States’ domestic oil shale resource has been given significant
consideration as a viable source for domestic fuel. Emphasis is placed on the
idea that the most important and direct factor in petroleum generation is a change
in the molecular structure of kerogen with increasing maturation. The most
straightforward method for determining source-rock potential is the Rock-Eval
pyrolysis method, but its accuracy is questioned (Espitalie et al, 1977). Samples
in this study range across a gradient of thermal maturity are of similar marine
origin. The objective of this study is (1.) to correlate chemical composition
changes between 13C NMR and Rock Eval pyrolysis and (2.) investigate the
potential advantages of using both techniques as a tool for source rock
evaluation.
Immature surface oil shales (<2500m) have the a potential to produce
approximately 1.5 TBOE in the United States and 3.4 TBOE worldwide through
retort methods (BP Statistical Analysis). Hence the need for an accurate source
rock evaluation.
Rock-Eval PyrolysisSolid-State 13C NMR
• Increasing Hydrogen Index (HI) value with
decreasing aromaticity. HI.
• Strong negative correlation coefficient (r=-
0.979) that agrees with current view.
• Because the kerogen type is known (Type
II) it can be used to estimate the thermal
maturity of the rock.
• Subject samples to HCL-HF for
demineralization
• Analyze chemical composition of
kerogen using CP and DP 13C NMR
techniques.
• Quantify petroleum generation
potential and quality through
Rock-Eval Pyrolysis.
• Separate aromatic and aliphatic
carbon fractions and compare
with Hydrogen Index and S2
values.
• Simulate possible pyrolysis
outcomes from TOC and NMR
data.
Table 2. Percentage of three carbon types for 13C CP and DP NMR spectra of the kerogens
Table1: Results from Rock-Eval analyses
• Rock Eval measurements S2 and HI correlated with aromatic
and aliphatic carbon fractions in determining generative
potential and thermal maturity.
• 13C CP spectra of whole rock organic matter upon
demineralization. Kerogens are arranged in order of increasing
maturity.
r = -0.979
• A strong positive correlation (r=0.828)
between the aliphatic fraction and potential
generative portion of hydrocarbons.(S2)
• Generally, oil shale containing more
aliphatics tends to produce higher fractions
of oils than that having more aromatics
(Botto, 1996).
• Useful for determining the amount of
hydrocarbons released upon artificial
maturation.
• Among nondestructive spectroscopic analyses, NMR spectroscopy is especially suited to provide novel structural insight of kerogen
alteration (Mao 2010).
• Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity.
• Aliphatics show to a strong correlation in relation to the amount of hydrocarbons that will be released by thermal cracking.
• Combining these two techniques provides solid data on structural composition, organic matter type, quality and oil yields of kerogen.
• Current work is being tested on 9 samples of the Eagle Ford Formation to make estimations of Rock Eval values from aliphatic and aromatic
fractions.
Fig. 2. Plot of kerogen aromaticity versus Rock-Eval HI index. Modified
from Smernik 2006
Figure 3: CP and DP NMR spectra of kerogens. Smernik 2006
Smernik R. J., Schwark L. and Schmidt M. W. I. (2006) Assessing the quantitative
reliability of solid-state 13C NMR spectra of kerogen across a gradient of thermal
maturity. Solid state NMR 29, 312–321.
Mao Jindong 2010., Chemical and nanometer-scale structure of kerogen and its
change during thermal maturation. Soil Sci. Soc. Am. J. 64, 873–884.
Maciel, Gary 1979., improvement in correlation between oil yields and 13 C n.m.r
spectra. Fuel v 52 I, 2
We would like to thank Dr, Hockaday and Dr. Driese for support of this
topic. Thanks to Todd Longbottom and Ken Boling for data acquisition/
processing. We would also like to thank Baylor Department of Geology for
suport of future research.
Figure 4: Plot of kerogen aliphatic content versus potential release of hydrocarbons.
Figure 1: Typical chemical shift for 13 C NMR spectra
Figure 2: Rock Eval three stage schematic.