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| Titel |
CO2 injection into submarine, CH4-hydrate bearing sediments: Parameter studies towards the development of a hydrate conversion technology |
| VerfasserIn |
Christian Deusner, Nikolaus Bigalke, Elke Kossel, Matthias Haeckel |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077475
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| Zusammenfassung |
| In the recent past, international research efforts towards exploitation of submarine and
permafrost hydrate reservoirs have increased substantially. Until now, findings indicate that a
combination of different technical means such as depressurization, thermal stimulation
and chemical activation is the most promising approach for producing gas from
natural hydrates. Moreover, emission neutral exploitation of CH4-hydrates could
potentially be achieved in a combined process with CO2 injection and storage as
CO2-hydrate.
In the German gas hydrate initiative SUGAR, a combination of experimental and
numerical studies is used to elucidate the process mechanisms and technical parameters on
different scales. Experiments were carried out in the novel high-pressure flow-through system
NESSI (Natural Environment Simulator for sub-Seafloor Interactions). Recent findings
suggest that the injection of heated, supercritical CO2 is beneficial for both CH4 production
and CO2 retention.
Among the parameters tested so far are the CO2 injection regime (alternating vs.
continuous injection) and the reservoir pressure / temperature conditions. Currently,
the influence of CO2 injection temperature is investigated. It was shown that CH4
production is optimal at intermediate reservoir temperatures (8 Ë C) compared to
lower (2 Ë C) and higher temperatures (10 Ë C). The reservoir pressure, however,
was of minor importance for the production efficiency. At 8 Ë C, where CH4- and
CO2-hydrates are thermodynamically stable, CO2-hydrate formation appears to be slow.
Eventual clogging of fluid conduits due to CO2-rich hydrate formation force open new
conduits, thereby tapping different regions inside the CH4-hydrate sample volume for
CH4gas. In contrast, at 2 Ë C immediate formation of CO2-hydrate results in rapid and
irreversible obstruction of the entire pore space. At 10 Ë C pure CO2-hydrates can
no longer be formed. Consequently the injected CO2 flows through quickly and
interaction with the reservoir is minimized. Our results clearly indicate that the
formation of mixed CH4-CO2-hydrates is an important aspect in the conversion
process.
The experimental studies have shown that the injection of heated CO2 into the
hydrate reservoir induces a variety of spatial and temporal processes which result in
substantial bulk heterogeneity. Current numerical simulators are not able to predict
these process dynamics and it is important to improve available transport-reaction
models (e.g. to include the effect of bulk sediment permeability on the conversion
dynamics).
Our results confirm that experimental studies are important to better understand the
mechanisms of hydrate dissociation and conversion at CO2-injection conditions as a basis
towards the development of a suitable hydrate conversion technology. The application of
non-invasive analytical methods such as Magnetic Resonance Imaging (MRI) and Raman
microscopy are important tools, which were applied to resolve process dynamics on the pore
scale. Additionally, the NESSI system is being modified to allow high-pressure flow-through
experiments under triaxial loading to better simulate hydrate-sediment mechanics. This
aspect is important for overall process development and evaluation of process safety issues. |
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