25th International Meeting on Organic Geochemistry IMOG 2011

P-361
H2S risking toolset – thermochemical sulphate reduction field
study and analytical efforts: Sequential diagnostics for Fluidfluid-rock
interactions
Henning Peters 1 , Olaf G. Podlaha 1 , Erdem Idiz 1 , Chad Glemser 2 , Lavern Stasiuk 2 , Volker
Dieckmann 1
1 Shell Global Solutions <strong>International</strong> B. V., Rijswijk, Netherlands, 2 Shell Canada Energy, Calgary, Canada
(corresponding author:Henning.Peters@shell.com)
The distribution of non-hydrocarbon ―sour‖ gases
(H2S, CO2) in hydrocarbon reservoirs is controlled
mainly by thermochemical sulphate reduction (TSR)
and organic matter cracking of organic sulfur
compounds (OSC) in high temperature reservoirs
versus bacterial sulfate reduction (BSR) in lowtemperature
reservoirs.
In this study we focus on TSR, which is by far the
most important process in the subsurface for the
generation of significant levels of H2S. Over the past
years continuous progress has been made in the
understanding of chemical mechanisms, major
catalysts, temperature thresholds and kinetics for the
generation of H2S from TSR, [1], [2], [3], [4]. However,
the complexity of sulphur chemistry and water-rock
interaction limits our ability to extrapolate from
experimental data to field scale. On how that can be
translated into predicitive capabilities we refer to [5].
Consequently, understanding and risking H2S
formation in the subsurface begins with the use of
diagnostic tools 1) to approximate the H2S source, 2)
gather lateral and vertical subsurface variabilities, 3)
to relate the degree of H2S variability to chemical
process and subsurface conditions including the
interaction with fluids and rock matrix.
We present the main elements of a diagnostic
workflow that was developed and is in more detail
explained in [5] to first understand and then quantify
the subsurface distribution of H2S.
Throughout the TSR process the natural incorporation
of sulphur into bitumen (natural vulcanization) was
investigated to elucidate the evolution of H2S
formation in using sulphur compound class
distributions.
The field studies were supported by a sequence of
analytical efforts including:
- 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 newly gathered workflow data compared with
production data reveal good correlation to support the
approach.
The workflow was developed on stacked Upper
Devonian to Mississippian sour gas reservoirs
situated in the Rocky Mountains Foothills of Alberta,,
Western Canadian Sedimentary Basin (WCSB),
Canada. Production from these reservoir units is
mainly dry gas and different forms of sulfur. H2S
contents ranging from 5% to almost 90% were
studied. Prolonged history in production data
combined with the close proximity of reservoir
intervals with different levels of H2S are excellent
natural laboratories to reveal the main drivers of its
distribution resulting from TSR.
[1] Zhang et al. (2007): Org. Geochem. 38, 897-910.
[2] Kelemen et al. (2010): GCA 74, 5305-5332.
[3] Ma et al. (2008): GCA 72, 4565-4576.
[4] Machel (2001): Sed. Geol. 140, 143-175.
[5] Podlaha et al. (2011): This abstract volume
491