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Nondestructive natural gas hydrate recovery driven by air and carbon dioxide.

Kang H, Koh DY, Lee H - Sci Rep (2014)

Bottom Line: Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases.Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH.The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea.

ABSTRACT
Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH₄-air or CH₄-CO₂/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

No MeSH data available.


Related in: MedlinePlus

Decomposition/replacement ratio beyond the CMC observed under the conditions in the East Sea using CO2/air (20 mol% CO2 and 80 mol% air) gas.Black and yellow bars represent total CH4 recovery rates based on combination of decomposition and replacement in the pure GH and UBGH, respectively. When CH4 to CO2/air ratio exceeds the CMC, replacement between CH4 and CO2/air initiates. Shaded areas represent the fraction of replacement in the total CH4 recovery and solid lines represent relative contributions of replacement in each case.
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f6: Decomposition/replacement ratio beyond the CMC observed under the conditions in the East Sea using CO2/air (20 mol% CO2 and 80 mol% air) gas.Black and yellow bars represent total CH4 recovery rates based on combination of decomposition and replacement in the pure GH and UBGH, respectively. When CH4 to CO2/air ratio exceeds the CMC, replacement between CH4 and CO2/air initiates. Shaded areas represent the fraction of replacement in the total CH4 recovery and solid lines represent relative contributions of replacement in each case.

Mentions: To see patterns for mixed hydrates that have larger CH4-CO2/air mole ratios than at CMC, we carried out ex-situ HRPD experiments using the 9B beam line of the Pohang Accelerator Laboratory (see Supplementary Fig. S10). First, we determined the CMC of 0.418 in the ratio of CO2/air (2:8) and then observed the chemical exchange that occurred above the CMC. For comparison, the HRPD pattern at a CH4-air mole ratio of 2.53 is represented by the black line. From structural analysis we confirmed the coexistence of Structure I gas hydrate and hexagonal ice when either air or CO2/air was injected into the NGH and we obtained their relative amounts by entire-pattern fitting. The compositions of the sI gas hydrates were analyzed using GC. Thus the combined refined HRPD (ice to sI ratio) and GC results (replacement efficiency revealed by remaining gas composition in the hydrate phase) are shown as relative contributions of decomposition and replacement (Fig. 6). The detailed descriptions for the quantitative analysis can be found in Methods. CH4 recovery by decomposition is shown as gray bars and CH4 recovery by replacement is shown as shaded bars. The sum of these two bars is the rate of total CH4 recovery. Solid lines represent the ratio between ‘CH4 recovery by decomposition' and ‘CH4 recovery by replacement' in each sample. Interestingly, directly above the CMC, considerable amounts of CO2, N2, and O2 initiated replacement of CH4 in the NGH, even under harsh, deep-sea conditions. Particularly, we note that the contribution of replacement to NGH recovery (versus the contribution of decomposition) became more significant as the ratio of methane to CO2/air increased. Another notable feature is that the NGH production concept based on the CMC can be unrestrainedly applicable to a variety of geological settings with site-specific hydraulic pressures and geothermal gradients (red line in Fig. 6 shows UBGH sediment effect).


Nondestructive natural gas hydrate recovery driven by air and carbon dioxide.

Kang H, Koh DY, Lee H - Sci Rep (2014)

Decomposition/replacement ratio beyond the CMC observed under the conditions in the East Sea using CO2/air (20 mol% CO2 and 80 mol% air) gas.Black and yellow bars represent total CH4 recovery rates based on combination of decomposition and replacement in the pure GH and UBGH, respectively. When CH4 to CO2/air ratio exceeds the CMC, replacement between CH4 and CO2/air initiates. Shaded areas represent the fraction of replacement in the total CH4 recovery and solid lines represent relative contributions of replacement in each case.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196106&req=5

f6: Decomposition/replacement ratio beyond the CMC observed under the conditions in the East Sea using CO2/air (20 mol% CO2 and 80 mol% air) gas.Black and yellow bars represent total CH4 recovery rates based on combination of decomposition and replacement in the pure GH and UBGH, respectively. When CH4 to CO2/air ratio exceeds the CMC, replacement between CH4 and CO2/air initiates. Shaded areas represent the fraction of replacement in the total CH4 recovery and solid lines represent relative contributions of replacement in each case.
Mentions: To see patterns for mixed hydrates that have larger CH4-CO2/air mole ratios than at CMC, we carried out ex-situ HRPD experiments using the 9B beam line of the Pohang Accelerator Laboratory (see Supplementary Fig. S10). First, we determined the CMC of 0.418 in the ratio of CO2/air (2:8) and then observed the chemical exchange that occurred above the CMC. For comparison, the HRPD pattern at a CH4-air mole ratio of 2.53 is represented by the black line. From structural analysis we confirmed the coexistence of Structure I gas hydrate and hexagonal ice when either air or CO2/air was injected into the NGH and we obtained their relative amounts by entire-pattern fitting. The compositions of the sI gas hydrates were analyzed using GC. Thus the combined refined HRPD (ice to sI ratio) and GC results (replacement efficiency revealed by remaining gas composition in the hydrate phase) are shown as relative contributions of decomposition and replacement (Fig. 6). The detailed descriptions for the quantitative analysis can be found in Methods. CH4 recovery by decomposition is shown as gray bars and CH4 recovery by replacement is shown as shaded bars. The sum of these two bars is the rate of total CH4 recovery. Solid lines represent the ratio between ‘CH4 recovery by decomposition' and ‘CH4 recovery by replacement' in each sample. Interestingly, directly above the CMC, considerable amounts of CO2, N2, and O2 initiated replacement of CH4 in the NGH, even under harsh, deep-sea conditions. Particularly, we note that the contribution of replacement to NGH recovery (versus the contribution of decomposition) became more significant as the ratio of methane to CO2/air increased. Another notable feature is that the NGH production concept based on the CMC can be unrestrainedly applicable to a variety of geological settings with site-specific hydraulic pressures and geothermal gradients (red line in Fig. 6 shows UBGH sediment effect).

Bottom Line: Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases.Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH.The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Guseong-dong, Yuseong-gu, Daejeon 305-701, South Korea.

ABSTRACT
Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH₄-air or CH₄-CO₂/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

No MeSH data available.


Related in: MedlinePlus