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46720-AC2
Stable Carbon and Hydrogen Isotopic Relationships of Individual Saturated and Aromatic Hydrocarbons in Source Rocks and Petroleum
Kliti Grice, Curtin University of Technology
Dr Pierre Le Metayer
was appointed on 7th January 2008 to commence the ACS project. He
has completed the analytical separation (argentation
TLC) of a selection of Australian crude oils (20) their d13C analyses of individual
aromatic hydrocarbons are currently in progress. A further 15 (Australian petroleum
systems) into saturate, aromatic and polar fractions by liquid chromatography,
characterization of saturate and aromatic hydrocarbon fractions by GC-MS. We have also performed inorganic isotopes of the same
crude oils by a new method (Laser-ICP-MS) to compare with the Sofer plot as described in the proposal. We have also extracted and
separated extracts (including liquid chromatography and molecular sieving) from
the Williston Basin and Bakken
shale for D/H and 13C/12C analyses. The
application of D/H of biomarkers as a maturity parameter for Devonian
source-rocks from Western Canada Sedimentary Basin (WCSB) has been determined,
extending the application of D/H measurements to much older sediments than previously
studied. A mechanism has been proposed which can account for both H/D exchange,
and epimerisation of pristane and phytane
in the sedimentary environment. The effect of thermal maturation
sedimentary processes on the dD values of
individual petroleum hydrocarbons (n-alkanes and regular isoprenoids) over
geological timescales has been explored. Six different sedimentary
sequences have been studied to date covering a wide range of maturities, i.e.
0.53–1.6% vitrinite reflectance (Ro or
equivalent i.e. Re, Rc)
and ranging in age from the Lower Cretaceous to the Permian. In general the n-alkanes, pristane and phytane of relatively immature sediments have dD values that represent the accepted isotopic
composition of their natural product precursors, i.e. biosynthesised from n-alkyl
and isoprenoidal lipids. With increasing maturity, pristane and phytane become more
enriched in D, while the n-alkanes generally
remain at a constant isotopic composition, until a late-post mature level is
reached where there is a significant enrichment of D in n-alkanes. The enrichment of D in pristane
and phytane with increasing maturity correlates
strongly with changes in traditional maturity parameters including vitrinite reflectance and Tmax,
providing further evidence that D-enrichment is associated with thermal
maturation.
In addition, a new molecular
sieve method (Grice et al., 2008) has been employed in the above project. In this study a simplified 5A method that
avoids the use of HF has been developed to isolate n-alkanes
ranging from n-C7
to at least n-C30 from a saturated petroleum hydrocarbon fraction. 12 % of cyclohexane in n-pentane
as the extraction solvent was found to be sufficient in removing almost all the
n-alkanes
(>90%) from the 5A molecular sieve. By substituting cyclohexane
with cyclohexene it was
found that the cyclohexene had a negligible effect on
the extraction process, whereas cyclopentane worked
equally well. The new 5A sieve procedure is a rapid and safer procedure
for extracting all n-alkanes from petroleum to yield fractions amenable for
routine stable carbon isotope analysis.
Dr Pierre Le Metayer
has only been appointed for 8 months and has one conference abstract accepted.
We have 3 papers published or submitted related to the above research project.
AUD $51,742 was received and salary pay of $51,696 p.a. was
used for the project.
Peer-reviewed Publications
Maslen, E., Grice, K., Gale, J., Hallmann,
C. and Horsfield, B., 2008 Crocetane: A potential
marker of photic zone euxinia
in thermally mature sediments and crude oils of Devonian age. Organic Geochemistry accepted subject to
revisions.
Maslen E., Grice K., Dawson D., White,
D., Horsfield B., 2008, Stable hydrogen isotopes for assessing thermal history
of sediments through geological time Thermal history analysis of sedimentary
basins: methods and applications. U.S.
Geological Survey submitted.
Grice K., De Mesmay R., Wang, S. and de Glucina
A. 2008 New 5A molecular sieving method for
CSIA. Organic
Geochemistry 39,
284-288.
Conference presentations
Maslen, E., Grice, K., Gale, J, and
Horsfield, B. Crocetane: A marker for photic-zone euxinia in Devonian
source rocks (Duvernay formation, Western Canada Sedimentary Basin)
and crude oils. (EGU Conference, April 2008, oral presentation).
Maslen, E., Grice, K., Gale, J, and
Horsfield, B. The significance and origin of the biomarker crocetane
in Devonian source rocks and crude oils (Western Canada
sedimentary basin and Canning basin, WA). “Australian Earth Science
Convention” (AESC) Conference, Perth, WA, 2008).
Maslen, E., Grice, K., and Horsfield, B.
Significance of Crocetane in Devonian source-rocks
and crude oils from Duvernay Formation and Bakken Shale (AOG Conference, September 2008).
P. Le Métayer,
K. Grice, D. Dawson and B. van Aarssen. Stable carbon and
hydrogen isotopic relationships of individual saturated and aromatic
hydrocarbons in source-rocks and petroleum (AOG Conference, September 2008).
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