Application of 13C NMR Spectroscopy and DAC Pyrolysis to the Study of Oil Potential of Kerogens
Date Issued
2009
Date
2009
Author(s)
Mo, Hui-Jane
Abstract
A variety of maceral samples were characterized by the solid-state 13C CP/MAS NMR spectroscopy and their oil and gas generative potentials were evaluated by in-situ visual observations in a diamond anvil cell. The results show that exinite generated large amounts of visible oil-like liquid along with some gas, while fusinites generated no visible liquid and gas. The liquid (oil) from exinite appears light in color and less viscous. Some non-perhydrous vitrinite unexpectedly generated large amounts of visible liquid, although the liquid is darker and thicker than that from exinite, indicating that the oil potential of vitrinites is not limited to its perhydrous nature. The visual peak temperatures (Tpeak) of maximum rate of liquid petroleum generation for vitrinite (465-540°C) are generally higher than those for exinites (453-475°C). The results from NMR show that the aromaticities（fa） of macerals, which are the lowest in exinite and highest in fusinite, are inversely related to their oil generative capacities, which exhibits the highest oil generation potential for exinite. The observed linear relationship between the logarithms of fa values vs. %Ro suggests a potential maturity indicator. The dependence of NMR spectroscopy on organic maturity was further studied by artificially maturing two immatured keorgens from Green-River and Barnett shales and terrestrial coal. Isolated kerogen samples were pyrolyzed at 320°C in durations, equivalent to four levels of maturities（Ro = 0.79 , 0.95 , 1.10 , 1.34%） using confined-pressure (gold-tube) pyrolysis. Similar to those observed from macerals, the results show that the aliphatic groups in the matured kerogens decrease while aromatic groups increase significantly with increasing maturities. The fa values are positively correlated with the maturities among which the Green-River kerogen exhibited the highest effect. However, the fa values increase only subtle beyond a maturity equivalent to 1.1 %Ro for all three kerogens. The DAC pyrolysis of the matured samples reveals significant decrease in oil generation potential with maturity, particularly for the Barnett kerogen.
Subjects
13C NMR
diamond anvil cell
kerogen
maturity
Type
thesis
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