Analysis and characterization of samples from sedimentary strata with correlations to indicate the potential for hydrocarbons |
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Authors: | Hsien-Tsung Lee |
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Institution: | (1) Department of Electrical Engineering, Nan Kai University of Technology, Tsao Tun, Nan Tou County, Taiwan, ROC |
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Abstract: | The Rock-Eval pyrolysis and TOC analysis have been widely used to evaluate the source rock quality. The atomic H/C ratio of
kerogen, however, has been overlooked in source rock evaluation. In this study, coal and carbonaceous samples, including 26
from northwestern Taiwan, 12 from China, and 4 from the United States were analyzed, and integrated with 157 published data,
to explore the significance of atomic H/C ratio as a parameter of source rock evaluation. Two different linear trends were
observed in the cross-plot of S
1 versus S
2. Field outcropped shale or C-shale exhibits a steeper slope compared to that of coal samples which can be attributed to the
compositional difference in their organic material. A rather strong positive correlation for H% versus S
2 illustrates the contribution of H-containing macerals, especially exinite. Organic matters in the samples studied are of
type II/III kerogen based on the relationship between HI and T
max. The H/C ratio, as well as the HI, S
1, and S
2, generally decreases with the maturity increasing. The H/C ratio decreases slightly from 1.1 to 0.7 with the maturity increasing
from R
o 0.55 to 0.85%. Samples with H/C ratio in this range show significant change in certain other geochemical parameters (e.g.
HI, S
1, S
2, S
1 + S
2, S
1/(S
1 + S
2), S
1/TOC, (S
1 + S
2)/TOC, T
max). The (S
1 + S
2)/TOC ratio (defined as QI) was used as an indicator of the hydrocarbon potential. The QI, HI, and H/C ratio show a certain
correlation, all increasing accordingly. The QI of the samples analyzed in this study is approximately 100–380 (mgHC/gTOC),
similar to that of most humic coals for oil and gas generation. Samples with R
o value lower than 0.55% always show significant variation in their HI, ranging from 80 to 520 mgHC/gTOC. It is inferred that
hydrocarbon potential started from R
o 0.55% and atomic H/C ratio 1.1 in this study. |
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Keywords: | |
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