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| Titel |
Contribution of terrigenous rocks of South Belgian coal deposits in geological storage of CO2 : the sandstones case |
| VerfasserIn |
N. Dupont, J.-M. Baele |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030584
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| Zusammenfassung |
| Sequestration of CO2 in unmined coal seams is one of the different options for storing CO2 in
geological reservoirs. In favorable situations, it could be coupled with the retrieving of
adsorbed methane from coal (ECBM), which can make this solution economically more
attractive. However, in the case of South Belgian coal measures, both weak permeability of
the coal and frequent faulting/folding of the seams are likely to decrease the efficiency of this
technique.
Westphalian A and B sediments from South Belgium are containing only about 2.5% vol.
of coal; the other rocks consisting of shales/siltstones (~80%) and sandstones (~20%). For
all these lithologies, the main processes of CO2 sequestration are 1) adsorption in coal and
clay minerals that are partly forming shales, and within rock porosity in the case of
sandstones and, to a lesser extent, in the shales/siltstone porosity. In a previous
assessment of the sequestration potential in Westphalian coal measures of South Belgium,
Baele et al. (2007) showed that coal and shales each account for 25% of the total
sequestration potential, and the rest, i.e. 50%, is related to sandstones on a basis of 2%
porosity.
Beside their significant additional storage capacity, sandstones have also a better
permeability than the other finer-grained and organic lithologies. Additionally,
sandstones are known to occasionally cut the coal seams (wash-out), thus providing
insights in increasing accessibility of injected CO2 into the coal. On the other hand,
some sandstone banks are fossil braided rivers that induced peripheral fractures
by differential compaction during burial diagenesis (Van Tongeren et al., 2000).
These fractures are thus likely to have increased accessibility from high-injectivity
sandstones to surrounding lithologies that could significantly contribute to storage
capacity.
The aim of this study is to refine the contribution of the westphalian South Belgium
sandstones to the geological storage of CO2. Measurements were performed on forty rock
samples in order to determine their mineral compositions and petrophysical properties.
Mineral compositions were determined by light and cathodoluminescence petrography (CL),
XRD, SEM, EDS and TOC. Effective porosity and permeability were measured by lab tests
on cylindrical core samples.
Effective porosities measured in sandstones is ranging between 1.5% and 6% with an
average of 3.5%, which is nearly twice the value taken in the previous capacity evaluation.
The neutron porosity log of the Saint-Ghislain borehole yields porosity values ranging
between 5 and 20% of limestone-equivalent porosity; these values suggest higher in-situ
porosity, likely due to fractures in the coal measures.
Permeability was estimated from lab permeameter tests to a few milli-darcies.
Nevertheless this value, which is fairly low for a conventional reservoir, is higher than that of
other Westphalian lithologies. Like porosity, in-situ permeability is expected to be
higher.
Westphalian sandstones mineral compositions shows mainly quartz, feldspars, clay
minerals, coal grains that are cemented by either quartz overgrowth or a matrix consisting of
fine detrital (mainly clays) and alteration minerals (authigenic carbonates, pyrite, and clays).
These results are comparable to investigations of Westphalian C and D sandstones of North
Belgium (Bertier et al., 2006). In the case of Westphalian sandstones, it was observed that the
effective porosity is essentially located within this fine-grained matrix, explaining their weak
permeability.
Results from this study show other promising insights for the sequestration of CO2
within Westphalian sandstones of South Belgium. Carbonate minerals, which occur
with 2% vol. in average, could significantly increase the porosity and especially
the permeability, due to their dissolution by water acidification caused by CO2
injection. Adsorption onto coal fragments and clay minerals in the sandstones has an
estimated sequestration potential similar to that of storage in rock porosity. Finally, for
reservoir safety purpose, a preliminary assessment of the mineral trapping potential
shows that the whole sequestrated CO2 (within the porosity and by adsorption)
could react with CO2-sensitive minerals such as chlorites and feldspars in the long
term.
References :
Baele J.M., Raucq V. , De Weireld G., Legrain H., Billemont P., Tshibangu K. & Dupuis
C. (2007) - Geological Storage of CO2 : New Concepts from Storage Capacity Evaluation in
Belgian Westphalian Rocks - EGU Meeting, Vienna 2007.
Bertier P., Swennen R., Laenen B., Lagrou D. & Dreesen R (2006) - Experimental
identification of CO2–water–rock interactions caused by sequestration of CO2 in Westphalian
and Buntsandstein sandstones of the Campine Basin (NE-Belgium) – Journal of Geochemical
Exploration 89 (2006) : 10-14.
Van Tongeren P., Laenen B. & Dreesen R. (2000) - Het koolbedmethaanpotentieel in
Vlaanderen en de mogelijkheden tot geologische opslag van CO2 in relatie tot de winning
van deze gasreserves: een pré-haalbaarheidsstudie t.b.v. de Administratie Natuurlijke
Rijkdommen en Energie. VITO report 2000/ETE/R/028, 100 pp. |
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