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@PHDTHESIS{Khajooie:1004346,
author = {Khajooie, Saeed},
othercontributors = {Littke, Ralf and Busch, Andreas},
title = {{E}xperimental investigation of porosity, surface area, and
gas diffusivity impacts on methanogenic activity within
porous media: implications for underground hydrogen storage},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2025-01375},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2025; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2024},
abstract = {AbstractThe transition from fossil fuels to renewable
energy sources has significantly increased interest in
large-scale hydrogen (H2) storage within subsurface
formations. This strategy addresses the intermittency issues
of renewable energy caused by atmospheric fluctuations,
leading to an imbalance in energy supply and demand. Surplus
energy can be converted to H2 via water electrolysis and
then stored in various geological formations, including
depleted oil and gas reservoirs, saline aquifers, and salt
caverns. However, injecting H2 into subsurface formations
may stimulate microbial metabolism, potentially leading to
the irreversible conversion of H2 into byproducts like CH4,
H2S, and acetic acid, posing risks of H2 contamination and
equipment corrosion. Despite these challenges, the potential
to convert H2 into CH4 through biological processes, a
technique known as bio-methanation, presents an opportunity
for sustainable underground methane production.This work
aimed to explore the impact of pore characteristics on
methanogenic activity within porous media. The model
organism was Methanothermococcus thermolithotrophicus, a
strain of methanogenic Archaea. Reservoir analogues from the
Cretaceous (Bentheim Sandstone, Obernkirchen Sandstone,
Anröchter Grün Limestone) and Triassic (Red and Grey Weser
Sandstone) were selected for this study based on their
differences in porosity (8-24 $\%).$ The results of Chapter
2 demonstrate the influence of sand particles, rock
fragments, and porous rocks on methanogenic activity,
setting the stage for detailed experimental investigations.
Measurements on water-saturated rock specimens revealed a
strong correlation between microbial activity and pore
volume. Additionally, the higher activities observed in
intact rocks compared to their corresponding bulk solutions
(8-10 times higher) indicate that the available surface area
for microbial colonization is a crucial factor in
controlling microbial activity when the amount of substance
is constant. With the cell size of the utilized Archaea
ranging from 1 to 2 µm, only pores larger than this
threshold are accessible. This conclusion is further
supported by increased activities in the presence of sand
particles and rock fragments compared to their respective
bulk solutions, as well as variations in activities within
water-saturated rocks with similar pore volumes. In Chapter
3, various techniques including mercury injection capillary
pressure (MICP), nuclear magnetic resonance (NMR), scanning
electron microscopy (SEM), and X-ray micro-computed
tomography (µCT) were employed to assess the impact of
surface area quantitatively. The specific surface area of
accessible pores obtained from MICP, NMR, and SEM revealed
strong correlations with the normalized microbial activity,
confirming the role of surface area in accelerating
methanogenic reactions. The normalization procedure accounts
for pore volume and gas-liquid interfacial area. The impact
of interfacial area and, consequently, mass transfer flux
has been observed through the higher activity of Grey Weser
sandstone compared to Bentheim sandstone, as measured in the
test conducted on rocks with similar pore volumes. Grey
Weser sandstone exhibits a lower specific surface area of
accessible pores but a larger interfacial area. Chapter 4
examines the effective diffusivity of gas in water-saturated
rock specimens, a crucial parameter in governing gas-liquid
mass transfer. The rate of methanogenic reactions depends on
the amount of H2 and CO2 molecules in the aqueous phase,
suggesting an indirect influence of the mass transfer
process on microbial activity. The experiments were
conducted using the pressure decay technique under initial
pressure and temperature of 1.0 MPa and 35°C, respectively.
The analyzed rock specimens exhibited effective H2
diffusivity ranging from 0.8∙10-9 to 2.9∙10-9 m²/s,
which is higher than the respective values for CH4 and CO2,
ranging from 0.3∙10-9 to 0.9∙10-9 m²/s. Additionally,
it was observed that effective diffusivities positively
correlate with other rock properties such as porosity,
permeability, and mean pore radius.The findings of this
thesis hold significant implications for integrating pore
characteristics into existing kinetic microbial growth
models such as the Monod or Contois (Muloiwa et al., 2020),
enabling more accurate estimations of microbial activities
during both underground hydrogen storage and underground
bio-methanation.},
cin = {532410 / 530000},
ddc = {550},
cid = {$I:(DE-82)532410_20140620$ / $I:(DE-82)530000_20140620$},
pnm = {BMBF 03G0870C - H2ReacT - Transport von Wasserstoff in
Gesteinen unter Berücksichtigung abiotischer chemischer und
mikrobieller Redoxreaktionen (03G0870C) / BMBF 03G0902C -
H2ReacT2 - Transport von Wasserstoff in Gesteinen unter
Berücksichtigung abiotischer chemischer und mikrobieller
Redoxreaktionen (03G0902C)},
pid = {G:(BMBF)03G0870C / G:(BMBF)03G0902C},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2025-01375},
url = {https://publications.rwth-aachen.de/record/1004346},
}
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