TY - JOUR
T1 - Position-specific carbon and hydrogen isotopic compositions of propane from natural gases with quantitative NMR
AU - Liu, Changjie
AU - McGovern, Gregory P.
AU - Liu, Peng
AU - Zhao, Heng
AU - Horita, Juske
N1 - Funding Information:
We thank Gérald Remaud, Serge Akoka, and other scientists from the University of Nantes for their advices on method developments. We thank oil companies (Chesapeake Energy, Pablo Energy II LLC, and Napier Engineering) and Toti Larson (Bureau of Economic Geology, The University of Texas at Austin) for their help on sample collection. Financial support was provided by ACS-PRF ( 51786-ND2 ) and U.S. Department of Energy Geosciences program ( DE-SC0016271 ). NMR facilities used in this study were supported by National Science Foundation Grant 1048553 (Texas Tech University) and 1428605 (West Texas A&M University). We would like to thank the reviewers for their valuable comments to improve the quality of the paper.
Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/7/5
Y1 - 2018/7/5
N2 - Position-specific isotope compositions of light hydrocarbons are expected to provide valuable information on their formation and migration-degradation processes. Here we present a high-accuracy and high-precision (≤±10 and ≤±1‰ for 2H and 13C isotope compositions, respectively) method to determine position-specific hydrogen and carbon isotope compositions of propane from natural gases with quantitative NMR. Customized, light-weight high-pressure sapphire NMR cells were developed for liquefied propane samples. Precision and accuracy of our technique were demonstrated using 13C-labeled compounds, neat samples of C3-C5 with natural isotope abundances, and inter-laboratory comparison of a C7 sample. To determine position-specific isotope compositions of propane from natural gas samples, a method was developed to collect and purify large amount (~6.8 mmol) of propane, using a variable-temperature cold trap. A test with a synthetic sample of natural gas mixture indicates that little isotope fractionation occurred during the propane separation and purification from natural gas mixtures. For the first time, high-precision and high accuracy data are reported of position-specific carbon and hydrogen isotope compositions of propane from different sources, including conventional and unconventional petroleum reservoirs. Preliminary results show that position-specific isotope fractionations between the center and terminal sites of propane vary widely for the different sources. Position-specific isotope compositions of propane have the potential to improve our understanding on the origins, migration and degradation processes of natural gas and hydrocarbons in general.
AB - Position-specific isotope compositions of light hydrocarbons are expected to provide valuable information on their formation and migration-degradation processes. Here we present a high-accuracy and high-precision (≤±10 and ≤±1‰ for 2H and 13C isotope compositions, respectively) method to determine position-specific hydrogen and carbon isotope compositions of propane from natural gases with quantitative NMR. Customized, light-weight high-pressure sapphire NMR cells were developed for liquefied propane samples. Precision and accuracy of our technique were demonstrated using 13C-labeled compounds, neat samples of C3-C5 with natural isotope abundances, and inter-laboratory comparison of a C7 sample. To determine position-specific isotope compositions of propane from natural gas samples, a method was developed to collect and purify large amount (~6.8 mmol) of propane, using a variable-temperature cold trap. A test with a synthetic sample of natural gas mixture indicates that little isotope fractionation occurred during the propane separation and purification from natural gas mixtures. For the first time, high-precision and high accuracy data are reported of position-specific carbon and hydrogen isotope compositions of propane from different sources, including conventional and unconventional petroleum reservoirs. Preliminary results show that position-specific isotope fractionations between the center and terminal sites of propane vary widely for the different sources. Position-specific isotope compositions of propane have the potential to improve our understanding on the origins, migration and degradation processes of natural gas and hydrocarbons in general.
KW - Natural gas
KW - Position-specific isotope analysis
KW - Propane
KW - Quantitative NMR
UR - http://www.scopus.com/inward/record.url?scp=85047554202&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2018.05.011
DO - 10.1016/j.chemgeo.2018.05.011
M3 - Article
AN - SCOPUS:85047554202
SN - 0009-2541
VL - 491
SP - 14
EP - 26
JO - Chemical Geology
JF - Chemical Geology
ER -