IAPETUS
doctoral training partnership
Novel Application of Sulfur and Re-Os Isotope Systematics to Aid
Exploration and Recovery of High Sulfur Bearing Petroleum
University of St Andrews, Department of Earth &
Environmental Sciences In partnership with Durham University,
Department of Earth Sciences and Shell International B.V.
Supervisory Team
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Key Words
Dr Harry Oduro, University of St Andrews,
http://earthsci.st-andrews.ac.uk/profile_hdo.aspx
E-mail: [email protected]
Dr David Selby, Durham University,
https://www.dur.ac.uk/earth.sciences/staff/academic/?id=2697
E-mail: [email protected]
1. Multiple sulfur isotopes, Re-Os Geochronology, Petroleum
source rocks, Thermochemical sulfate reduction (TSR), Oil
maturation and alteration.
Overview
Sulfur (S), after carbon(C) and hydrogen (H), is the
third most abundant element in petroleum, occurring
at concentrations of over 14% in some heavy oils.
Reserves of low sulfur crude oils are depleting
worldwide, which has necessitated increasing use of
crude oils with high sulfur content [1] but only under
strict constraints imposed by increasingly stringent
governmental limits on the sulfur contents of oils.
This project will focus on using a novel combination of
distribution and behaviour in the genesis
petroleum, and timing of source-to-sink pathway.
The condensation and polymerization of organic
matter into kerogen and bitumen is one of the key
steps in petroleum formation, as it ultimately
determines whether petroleum hydrocarbons will be
matured, altered, or preserved and buried in marine
sedimentary sandstone oil and gas reservoirs. In those
environments, a number of processes are involved in
which sulfur plays key roles, for example:
 seawater sulfate and sedimentary sulfur species
(e.g, sulfide (H2S), polysulfide (Sn2-), and elemental
sulfur (S8)) formed from bacteria sulfate reduction
(BSR) act to cross-link organic monomers to form
organosulfur compounds [2]; such a geochemical
evolution can be tracked using novel S-isotopes of
Δ33S versus δ34S as shown by the plot on the left
for data from the Monterey Fm and Ghareb
Limestone petroleum source rocks (PSR; these
Δ33S values, at 1σ uncertainty, indicate the
evolution of thiyl (RS-) and the sulfur
transformation via H2S production);
 the reaction of sulfate (SO42-) to hydrogen sulfide
(H2S) via thermal recovery and hydrous pyrolysis
can occur during thermochemical sulfate
reduction (TSR) [3,4]:
3SO42- + 4 RCH3
S-isotopes and Re-Os geochronology to understand
better the processes that influence sulfur’s
of
H2S (Low Conc.)
Temp. & Press.
3 S2- + 4 CO2 + 4 RH + 4 H2O
In both pathways, BSR and TSR, sour gas (CO2 + H2S)
can be formed [4,5], which can lead to severe
problems in the recovery and manufacturing of crude
oil, including: 1) detrimental effects on refining
catalysts, corrosion of pipes; 2) environmental impact
through acid rain caused by the release of sulfur
dioxide and 3) degrading the qualities of the crude oil
by the presence of recalcitrant polyaromatic sulfur
hydrocarbons catalysts, corrosion of pipes and their
environmental impact through acid rain caused by the
release of sulfur dioxide [5,6]. Mineral matrix and
other components in the petroleum source rocks can
also have a major effect on the course of TSR
reactions. For example, clays and metal sulfides, can
catalyze the reaction of H2S with organics to form S8
and altered hydrocarbons [6]. Although this reaction
is not sulfate reduction, it does point out that the
metals (e.g., Fe, Re and Os) and sulfur matrix
interact with the hydrocarbon fractions and can
provide information about the evolution, migration,
and alteration of the hydrocarbon products.
Thus, this project will address a key gap in our
knowledge of sulfur species and its associated metals
during the processes that determine their abundance,
distribution, and chemical combination (forms) in both
the formation and alteration of kerogen and bitumen.
Understanding the geochemistry of sulfur-rich
resources by coupling multiple S-isotopes with
rhenium–osmium (Re–Os) geochronometry in
kerogen, bitumen and the asphaltene of petroleum
and their source rocks is central to any strategy to
meet future energy demands of sulfur fuel oils.
In this proof of principle study, we propose to
investigate:
1. The partitioning and distribution of inorganic sulfur
species into specific organo-sulfur compounds in
petroleum source rocks and their thermal maturation
run products using high precision multi-sulfur isotope
measurements to truly ascertain is S-isotope
compositions can be used for oil fingerprinting [7].
2. Assess where Re and Os isotopes reside in kerogen,
bitumen and the asphaltene of petroleum during TSRto fingerprint oil to source rocks, the timing of oil
generation, and the mechanisms behind the resetting
of the Re-Os radioisotope clock by TSR reaction [8].
3. The geochemistry of sulfur radical chemistry in
kerogen source rocks and selected light hydrocarbon
products that is considered to be an important control
on petroleum maturation since S-S and C-S bonds are
more easily cleaved than carbon-associated bonds [9].
Combining the date from these approaches will
enhance understanding of sulfur transformations
associated with TSR during petroleum formation and
alteration and underpin development of methods
using sulfur and Re-Os isotope geochronometry as
aids in predicting the distribution of oils with high or
low sulfur contents.
This, then, will be used to better understand
and document the formation of sulfur compounds and
their radical chemistry in petroleum genesis and use
that knowledge to develop more efficient
biodesulfurisation (BDS) processes leading to more
environmentally sound and cost effective methods of
refinement of sulfur-bearing petroleum exploration.
Results of this research will have significant impact
over the next decade and beyond on sulfur-bearing
hydrocarbon
exploration
and
will
enhance
collaboration between academia and the petroleum
industry. This research will also transfer cutting-edge
knowledge from academia to the energy industry
thereby benefitting that industry by providing new
insights for enhancing energy supplies worldwide.
Methodology
A laboratory experiment and field-based methodology
will be employed to address the above questions. The
purpose of these experiments is to reproduce the
thermal maturation process that occurs in nature in a
controlled setting. Such experiments have been
extensively employed to understand the process of
source rock maturation, petroleum generation,
elemental partitioning between source and oil and
organic geochemistry. The TSR and hydrous pyrolysis
experiments will be conducted on both mature and
immature source rocks to track their thermal
maturation levels. Prior to themochemical pyrolysis
the various source rocks will be investigated for their
quadruple sulfur (δ34S, 33S, and 36S) and Re-Os
(187Re/188Os) abundances and isotope compositions.
The source rock will then be subjected to thermolysis
and pyrolysis experiments following the protocols of
[3] and [7]. After these experiments both the oil and
residual rock samples will be analysed in order to
establish if thermal maturation affected the S and ReOs abundances and isotope compositions.
To better simulate natural thermal maturation
of TSR reactions in petroleum systems we will employ
model sulfur compounds (e.g. sulfate, disulfide,
aromatic trithiane) to investigate the conditions under
which sulfur-centered radicals can be generated from
thermolysis reactions. We want to quantify as much
as possible each step of the fractionation process and
33S-isotope effect in reservoir source rocks to gain
insight to how sulfur radicals influence the cracking of
S-bearing hydrocarbons under thermal conditions.
To complement the lab-based study a fieldbased programme will focus on well-characterised
petroleum systems in which the source of oil is firmly
established; these are the Kimmeridge clay, Ghareb
Limestone and North Capsian basin. These systems
have been extensively researched and the sulfur, and
metal contents, kerogen types, and asphaltene and
butimen fractions in the source rocks are well known.
Timeline
Year 1: Geochemical and rock-eval characterisation of
source rocks. Chemical extraction of various Sspecies as well as Re, and Os for isotopic analyses.
Year 2: Hydrous pyrolysis and TSR experiments of
source rocks and model sulfur compounds.
Publication paper 1, and attending international
geochemistry conference.
Year 3: Application of laboratory measurements to a
well characterized petroleum system.
Year 4: Research dissertation and further papers.
Training & Skills
The student will be trained in various cutting-edge
geochemical and isotopic techniques and experiments
in extracting organic-inorganic S, as well as Re and Os
abundances in petroleum and source rocks The
training will also involve traditional methods for
characterising those materials such as rock-eval,
vitrinite reflectance, TOC, and biomarker analyses.
The student will also receive training and knowledge
in petroleum industry technologies at Shell
International Exploration and Production B.V., The
Hague, Netherlands (see attached letter). The skills
acquired during the studentship will be invaluable for a
career in either industry or academia and will give the
individual the confidence to interact with both
environments.
References & Further Reading
[1] Orr WL. & Sinninghe Damsté JS. 1990. ACS,
Chapter 1: 2–29.
[2] Vairavamurthy A. & Mopper K. 1987. Nature,
329, 623-625.
[3] Amrani A. et al. 2005, Geochimica et
Cosmochimica Acta, 69, 5317-5331.
[4] Goldstein TP. and Aizenshtat Z. 1994,
Journal Thermal Analysis, 42, 241-290.
[5] Mohebali G. & Ball AS. 2008. Microbiology, 154,
2169–2183.
[6] Machel HG. 200. Sedimentary Geology, 140,
143-175.
[7] Oduro et al. 2011. PNAS, 108, 17635-17638.
[8] Lillis PG. & Selby D. 2013. Geochimica et
Cosmochimica Acta, 118, 312-330.
[9] Lewan MD. 1998, Nature, 391, 164-166.
Further Information
Dr Harry Oduro, [email protected]
Laboratory for Isotope & Petroleum Geochemistry
Department of Earth and Environ. Sciences
University of St Andrews, Irvine Building, Room 422
St Andrews, Fife KY16 9AL, UK
Tel: +44 (0)133 4462819.
Dr David Selby, [email protected]
Department of Earth Sciences
University of Durham, Science Labs,
Durham DH1 3LE, UK
Tel: +44 (0)191 3342294.