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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

Direct visualization of guest-exchange analyzed by the Raman spectra after the injection of CO2/air (20 mol% CO2 and 80 mol% air) into pure CH4 hydrate (a–d) and NGH (e–h).CO2/air injection was performed at 288.15 K and 200 bar. As the CH4-CO2/air ratio increased, significant encapsulation of CO2, N2, and O2 molecules in the hydrate cages were detected. (a, e) C-O stretching and bending vibrational modes of CO2 molecules in the large cages of the hydrate; (b, f) C-H stretching vibrational modes of CH4 molecules in the hydrate; (c, g) N-N stretching vibrational modes of N2 molecules in the hydrate; (d, h) O-O stretching vibrational modes of O2 molecules in the hydrate.
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f3: Direct visualization of guest-exchange analyzed by the Raman spectra after the injection of CO2/air (20 mol% CO2 and 80 mol% air) into pure CH4 hydrate (a–d) and NGH (e–h).CO2/air injection was performed at 288.15 K and 200 bar. As the CH4-CO2/air ratio increased, significant encapsulation of CO2, N2, and O2 molecules in the hydrate cages were detected. (a, e) C-O stretching and bending vibrational modes of CO2 molecules in the large cages of the hydrate; (b, f) C-H stretching vibrational modes of CH4 molecules in the hydrate; (c, g) N-N stretching vibrational modes of N2 molecules in the hydrate; (d, h) O-O stretching vibrational modes of O2 molecules in the hydrate.

Mentions: Now we will focus on extending the phenomenological concept of air-based NGH decomposition to the CH4-CO2/air approach. Carbon dioxide is known to be a strong hydrate former and thus carbon dioxide mixed with air (20 mol% of CO2) slows the NGH decomposition rate. We note that the CMC is dramatically lowered to 0.418 when CO2 is added as a second guest (solid diamond in Fig. 1b). Fig. 3 shows the incorporations of N2, O2 and CO2 into the gas hydrate structure when the ratio of CH4-CO2/air exceeds CMC. Furthermore, we conducted the same experiment using real UBGH samples from the core section of UBGH-2-6-C. SEM images of the sediments are presented in Fig. 4. When the CH4-to-CO2/air ratios are greater than 0.418, which is the CMC for CO2/air (20 mol% of CO2), incorporation of gases in the gas hydrate structure is observed in the both pure gas hydrate system (Fig. 3a–d) and the UBGH system (Fig. 3e–h). Each of eight figures is presented in Supplementary Fig. S1–8.


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

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

Direct visualization of guest-exchange analyzed by the Raman spectra after the injection of CO2/air (20 mol% CO2 and 80 mol% air) into pure CH4 hydrate (a–d) and NGH (e–h).CO2/air injection was performed at 288.15 K and 200 bar. As the CH4-CO2/air ratio increased, significant encapsulation of CO2, N2, and O2 molecules in the hydrate cages were detected. (a, e) C-O stretching and bending vibrational modes of CO2 molecules in the large cages of the hydrate; (b, f) C-H stretching vibrational modes of CH4 molecules in the hydrate; (c, g) N-N stretching vibrational modes of N2 molecules in the hydrate; (d, h) O-O stretching vibrational modes of O2 molecules in the hydrate.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Direct visualization of guest-exchange analyzed by the Raman spectra after the injection of CO2/air (20 mol% CO2 and 80 mol% air) into pure CH4 hydrate (a–d) and NGH (e–h).CO2/air injection was performed at 288.15 K and 200 bar. As the CH4-CO2/air ratio increased, significant encapsulation of CO2, N2, and O2 molecules in the hydrate cages were detected. (a, e) C-O stretching and bending vibrational modes of CO2 molecules in the large cages of the hydrate; (b, f) C-H stretching vibrational modes of CH4 molecules in the hydrate; (c, g) N-N stretching vibrational modes of N2 molecules in the hydrate; (d, h) O-O stretching vibrational modes of O2 molecules in the hydrate.
Mentions: Now we will focus on extending the phenomenological concept of air-based NGH decomposition to the CH4-CO2/air approach. Carbon dioxide is known to be a strong hydrate former and thus carbon dioxide mixed with air (20 mol% of CO2) slows the NGH decomposition rate. We note that the CMC is dramatically lowered to 0.418 when CO2 is added as a second guest (solid diamond in Fig. 1b). Fig. 3 shows the incorporations of N2, O2 and CO2 into the gas hydrate structure when the ratio of CH4-CO2/air exceeds CMC. Furthermore, we conducted the same experiment using real UBGH samples from the core section of UBGH-2-6-C. SEM images of the sediments are presented in Fig. 4. When the CH4-to-CO2/air ratios are greater than 0.418, which is the CMC for CO2/air (20 mol% of CO2), incorporation of gases in the gas hydrate structure is observed in the both pure gas hydrate system (Fig. 3a–d) and the UBGH system (Fig. 3e–h). Each of eight figures is presented in Supplementary Fig. S1–8.

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