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OS6B-4:TECHNICAL ASPECTS OF GAS HYDRATE CONVERSION AND SECONDARY GAS HYDRATE FORMATION DURING INJECTION OF SUPERCRITICAL CO2 INTO CH4-HYDRATE-BEARING SEDIMENTS
发布时间:2014-07-28
Christian DEUSNER， Nikolaus BIGALKE, Elke KOSSEL， Matthias HAECKEL
Helmholtz-Zentrum für Ozeanforschung Kiel, GERMANY
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 gas 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 this process, at least transiently, secondary mixed hydrate formation is putatively more important than pure CO2-hydrate formation. In situ measurements showed dynamic changes of local p-/T-gradients due to gas hydrate dissociation or dissolution and secondary gas hydrate formation. It is a current objective of our studies to elucidate rheological properties and gas exchange efficiencies of CO2-CH4 mixed fluids that approach equilibrium with gas hydrates. We will also present results from high-pressure triaxial experiments that study the effect of in situ CH4-CO2-hydrate conversion and secondary gas hydrate formation on sediment geomechanical parameters.
Helmholtz-Zentrum für Ozeanforschung Kiel, GERMANY
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 gas 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 this process, at least transiently, secondary mixed hydrate formation is putatively more important than pure CO2-hydrate formation. In situ measurements showed dynamic changes of local p-/T-gradients due to gas hydrate dissociation or dissolution and secondary gas hydrate formation. It is a current objective of our studies to elucidate rheological properties and gas exchange efficiencies of CO2-CH4 mixed fluids that approach equilibrium with gas hydrates. We will also present results from high-pressure triaxial experiments that study the effect of in situ CH4-CO2-hydrate conversion and secondary gas hydrate formation on sediment geomechanical parameters.
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