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Composition, peat-forming vegetation and kerogen paraffinicity of Cenozoic coals: relationship to variations in the petroleum generation potential (hydrogen index)

Petersen, Henrik Ingermann; Lindström, Sofie LU ; Nytoft, Hans Peter and Rosenberg, Per (2009) In International Journal of Coal Geology 78(2). p.119-134
Abstract
Coals with similar thermal maturity and from the same deposit normally show a considerable range in

petroleum generation potential as measured by the Hydrogen Index (HI). This variation may partly be

related to variations in plant input to the precursor mires and organic matter preservation. It is widely

accepted that some Cenozoic coals and coaly sediments have the potential to generate oil, which is related

to the coal's paraffinicity. Coal paraffinicity is not readily reflected in the bulk HI. In this paper, the

relationships between measured HI and coal composition, coal kerogen paraffinicity and floral input have

been investigated in detail for three sets of coals from... (More)
Coals with similar thermal maturity and from the same deposit normally show a considerable range in

petroleum generation potential as measured by the Hydrogen Index (HI). This variation may partly be

related to variations in plant input to the precursor mires and organic matter preservation. It is widely

accepted that some Cenozoic coals and coaly sediments have the potential to generate oil, which is related

to the coal's paraffinicity. Coal paraffinicity is not readily reflected in the bulk HI. In this paper, the

relationships between measured HI and coal composition, coal kerogen paraffinicity and floral input have

been investigated in detail for three sets of coals from Colombia/Venezuela, Indonesia, and Vietnam. The

samples in each coal set are largely of iso-rank. The petroleum generation potential was determined by

Rock–Eval pyrolysis. Reflected light microscopy was used to analyse the organic matter (maceral)

composition and the thermal maturity was determined by vitrinite reflectance (VR) measurements. The

botanical affinity of pollen and spores was analysed by palynology. Coal kerogen paraffinicity was

determined by ruthenium tetroxide-catalysed oxidation (RTCO) followed by chain length analysis and

quantification (mg/g TOC) of the liberated aliphatic chains. The coals are dominated by huminite, in

particular detrohuminite. Only the Vietnamese coals are rich in microscopically visible liptinite. The pollen

and spores suggest that the coals were derived principally fromcomplex angiospermmire vegetations, with

subordinate proportions of ferns that generally grew in a subtropical to tropical climate.Measured HI values

vary considerably, but for the majority of the coals the values lie between approximately 200 mg HC/g TOC

and 300 mg HC/g TOC. Aliphatics yielding monocarboxylic acids dominate in the coal kerogen, whereas

aliphatics yielding dicarboxylic acids are secondary. However, the dicarboxylic acids show that crosslinking

long-chain aliphatics are present in the kerogen structure. All studied coals are paraffinicwith C19–35

aliphatic chains in the kerogen, and the aliphatics in the range C25–35 show that the coals may have the

potential to generate waxy crude oil. The Indonesian coals are richest in long-chain aliphatics and are thus

potentially most oil-prone. Multivariate statistical analysis shows that for the present three sample sets

variations in HI are positively correlated to different combinations of the C10+ aliphatic chains in the

kerogen and the amount of detrohuminite + liptodetrinite and liptinite. Furthermore, part of the HI can be

attributed to hydrogen in compounds with less than 10 carbon atoms, which is the lowest alkyl detected by

RTCO analysis, thus representing a potential for generation of gas and light liquid hydrocarbons. The

measured HI is therefore not always a good indicator for humic coal's potential to source waxy oil. Vegetational influence (palynology) on the variation of HI cannot be shown within the investigated span of variance and for the present coals. However, it is likely that some of the range in measured HI values is caused by floral vairiations not revealed by the palynological analysis and to variations in the preservation of the organic matter. (Less)
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in
International Journal of Coal Geology
volume
78
issue
2
pages
119 - 134
publisher
Elsevier
external identifiers
  • scopus:61849151365
ISSN
1872-7840
language
English
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a3e87adc-6fe3-4c50-bc99-6a69548597ed (old id 1778821)
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@article{a3e87adc-6fe3-4c50-bc99-6a69548597ed,
  abstract     = {Coals with similar thermal maturity and from the same deposit normally show a considerable range in<br/><br>
petroleum generation potential as measured by the Hydrogen Index (HI). This variation may partly be<br/><br>
related to variations in plant input to the precursor mires and organic matter preservation. It is widely<br/><br>
accepted that some Cenozoic coals and coaly sediments have the potential to generate oil, which is related<br/><br>
to the coal's paraffinicity. Coal paraffinicity is not readily reflected in the bulk HI. In this paper, the<br/><br>
relationships between measured HI and coal composition, coal kerogen paraffinicity and floral input have<br/><br>
been investigated in detail for three sets of coals from Colombia/Venezuela, Indonesia, and Vietnam. The<br/><br>
samples in each coal set are largely of iso-rank. The petroleum generation potential was determined by<br/><br>
Rock–Eval pyrolysis. Reflected light microscopy was used to analyse the organic matter (maceral)<br/><br>
composition and the thermal maturity was determined by vitrinite reflectance (VR) measurements. The<br/><br>
botanical affinity of pollen and spores was analysed by palynology. Coal kerogen paraffinicity was<br/><br>
determined by ruthenium tetroxide-catalysed oxidation (RTCO) followed by chain length analysis and<br/><br>
quantification (mg/g TOC) of the liberated aliphatic chains. The coals are dominated by huminite, in<br/><br>
particular detrohuminite. Only the Vietnamese coals are rich in microscopically visible liptinite. The pollen<br/><br>
and spores suggest that the coals were derived principally fromcomplex angiospermmire vegetations, with<br/><br>
subordinate proportions of ferns that generally grew in a subtropical to tropical climate.Measured HI values<br/><br>
vary considerably, but for the majority of the coals the values lie between approximately 200 mg HC/g TOC<br/><br>
and 300 mg HC/g TOC. Aliphatics yielding monocarboxylic acids dominate in the coal kerogen, whereas<br/><br>
aliphatics yielding dicarboxylic acids are secondary. However, the dicarboxylic acids show that crosslinking<br/><br>
long-chain aliphatics are present in the kerogen structure. All studied coals are paraffinicwith C19–35<br/><br>
aliphatic chains in the kerogen, and the aliphatics in the range C25–35 show that the coals may have the<br/><br>
potential to generate waxy crude oil. The Indonesian coals are richest in long-chain aliphatics and are thus<br/><br>
potentially most oil-prone. Multivariate statistical analysis shows that for the present three sample sets<br/><br>
variations in HI are positively correlated to different combinations of the C10+ aliphatic chains in the<br/><br>
kerogen and the amount of detrohuminite + liptodetrinite and liptinite. Furthermore, part of the HI can be<br/><br>
attributed to hydrogen in compounds with less than 10 carbon atoms, which is the lowest alkyl detected by<br/><br>
RTCO analysis, thus representing a potential for generation of gas and light liquid hydrocarbons. The<br/><br>
measured HI is therefore not always a good indicator for humic coal's potential to source waxy oil. Vegetational influence (palynology) on the variation of HI cannot be shown within the investigated span of variance and for the present coals. However, it is likely that some of the range in measured HI values is caused by floral vairiations not revealed by the palynological analysis and to variations in the preservation of the organic matter.},
  author       = {Petersen, Henrik Ingermann and Lindström, Sofie and Nytoft, Hans Peter and Rosenberg, Per},
  issn         = {1872-7840},
  language     = {eng},
  number       = {2},
  pages        = {119--134},
  publisher    = {Elsevier},
  series       = {International Journal of Coal Geology},
  title        = {Composition, peat-forming vegetation and kerogen paraffinicity of Cenozoic coals: relationship to variations in the petroleum generation potential (hydrogen index)},
  volume       = {78},
  year         = {2009},
}