Technical aspects of gas hydrate conversion and secondary gas hydrate formation during injection of supercritical CO2 into CH4-hydrate-bearing sediments

Deusner, Christian, Bigalke, Nikolaus, Kossel, Elke and Haeckel, Matthias (2014) Technical aspects of gas hydrate conversion and secondary gas hydrate formation during injection of supercritical CO2 into CH4-hydrate-bearing sediments [Paper] In: 8. International Conference on Gas Hydrates (ICGH8-2014), 28.07.-01.08.2014, Beijing, China.

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Abstract

The injection of CO2 into CH4-hydrate-bearing sediments has the potential to drive natural gas production and simultaneously sequester CO2 by hydrate conversion. Currently, process conditions under which this goal can be achieved efficiently are largely unknown. While the recent Ignik Sikumi field test suggests that a combination of N2/CO2 injection with depressurization yields effective CH4 production, in a previous study (Deusner et al., 2012) we showed that a combination of CO2 injection and thermal stimulation eliminates mass transfer limitations observed at cold reservoir temperatures. These high-pressure flow-through studies revealed that the injection of supercritical CO2 at 95 °C triggers dissociation of CH4-hydrates and counters rapid CO2-hydrate formation in the near-injection region. We also observed a strong effect of reservoir temperature on CH4 production and CO2 retention. The efficiency and yield of CH4 production was highest at a sediment temperature of 8 °C compared to 2 °C and 10 °C. At 2 °C CO2 hydrate formation was rapid and clogged the sediment at the injection spot. Outside the CO2-hydrate stability region, at 10 °C, we observed fast CO2 breakthrough and a comparably low CH4 production. Experiments comparing discontinuous and continuous CO2 injection showed that alternating periods of equilibration and CO2 injection improved the overall CH4 production. We hypothesize that slow formation of secondary CO2-rich hydrate improves the accessibility of the CH4-hydrate distributed in the sediment by locally changing permeability and fluid flow patterns. In situ measurements showed dynamic changes of local p-/T-gradients due to gas hydrate dissociation or dissolution and secondary gas hydrate formation. In addition, continued reconfiguration of guest molecules in transiently formed mixed hydrates maintain elevated gas exchange kinetics. Online effluent fluid analysis under in-situ pressure conditions indicated that CH4 released from CH4-hydrates is largely dissolved in liquid CO2.. It is a current objective of our studies to further elucidate rheological properties and gas exchange efficiencies of CO2-CH4 mixed fluids that approach equilibrium with gas hydrates and to study the effect of in situ CH4-CO2-hydrate conversion and secondary gas hydrate formation on sediment geomechanical parameters.

Document Type: Conference or Workshop Item (Paper)
Keywords: CO2 injection, hydrate conversion, chemical activation, supercritical CO2, gas hydrate reservoir, CH4 production
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Projects: SUGAR II
Date Deposited: 21 Nov 2014 10:39
Last Modified: 21 Dec 2016 08:00
URI: http://eprints.uni-kiel.de/id/eprint/26064

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