25th International Meeting on Organic Geochemistry IMOG 2011

O-11
Sulfur Rich Petroleum Systems: TSR and thermal cracking in
basin and reservoir field studies, simulation experiments and
model calibration
Olaf G. Podlaha, Henning Peters, Erdem Idiz, Volker Dieckmann
Shell Global Solutions <strong>International</strong> B.V., Rijswijk, Netherlands (corresponding
author:olaf.podlaha@shell.com)
Charge modelling and fluid property prediction in
petroleum system analysis relies on the integration of
field observations, appropriate simulation experiments
and risk reduction using up-to-date in-house modeling
tools. In complex systems such as Sulfur and its
inorganic and organic species in a petroleum system,
this approach allows us to accurately assess of a set
of key questions:
- How to model naturally observed Sulfur phases‘
variability as a result of (a) thermal cracking of
OM and (b) TSR processes ?
- How to model laboratory simulation experiments?
- How to use simulation experimental results for
generic process modeling?
- Which constraints from field studies will always
be needed to crosscheck models?
- Will modeling go beyond main fluid properties‘
prediction and allow for reconstruction of OM S
exchange reactions?
- Where is the boundary between a basin modeling
approach versus enhanced reservoir modeling
within the rock and brine framework?
In this study, a series of stacked Upper Devonian to
Mississippian sour gas reservoirs situated in the
Rocky Mountains Foothills of Alberta, Canada, serve
as natural labs. The Western Canadian Sedimentary
Basin (WCSB) is one of the most studied hydrocarbon
provinces in the world. Production from these
reservoir units is mainly dry gas and different forms
sulfur, with H2S contents ranging from 5% to almost
90% were studied. As a supplement, a Middle to
Upper Devonian condensate-sour gas reservoir (with
more than 35% H2S) in the Plains of Alberta was
investigated.
The field data studies [1] were supported
- Petrography (microscopy) of limestone and
dolostone in the petroleum reservoirs units
- Geochemical characterization of solid bitumen
using elemental analysis and X-ray absorption
spectroscopy (XANES)
- Carbon, oxygen and sulfur isotope analyses of
various phases
- Fluid inclusion studies using classic
microthermometry analysis and Raman
spectrometry for semiquantitative gas typing.
The results of this field study [1] were supplemented
by simulation experiments performing closed goldtube
pyrolysis to study the kinetics of both S-rich and
S-free OM thermal cracking in source rocks as well as
S-rich and S-free oil for a comparison of normal oil-togas-cracking
(OTGC) versus TSR controlled OTGC.
For OM thermal cracking it will be demonstrated that
the activation energies described in the literature for
hydreous and open pyrolysis experiments [2], [3]
differ from those obtained for gold tube pyrolysis,
though the general trend to lower activations energies
with increasing sulfur yield of the organic matter still
holds.
For TSR the role of catalysts such as Mg as well as
the importance of presence of different sulfur species
types for the onset and degree of TSR induced
hydrocarbon alteration as described in the literature
[4] will be shown in experiment and model results.
The simulation experiments furthermore suggest that
for higher maturities sulfur back-reaction at enhanced
TSR levels into aromatic hydrocarbon fraction allow
for the distinction of reactive and pyro-bitumen
forming hydrocarbon species.
As an outlook the importance of these results for the
modeling and prediction of fluid properties in S rich
petroleum systems will be demonstrated.
References
[1] Peters et al. (2011), this abstract volume
[2] Lewan and Ruble (2002), Org. Geochem., 33,
1457-1475
[3] Baskin and Peters (1992), AAPG Bull., 76, 1-13.
[4] Zhang et al. (2007), Org. Geochem., 38, 897-910
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