Raman Spectroscopic Studies of Methane Gas Hydrates

Hansen, Susanne Brunsgaard; Berg, Rolf W.

doi:10.1080/05704920802352614

Cited by 12 publications

(6 citation statements)

References 23 publications

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“…The frequency of C 2 H 6 in the I cage is almost equal to that in the gas phase. The agreement between the computed and experimental C−C vibrational frequencies support the inference that ethane can be trapped in the small 5 12 cage of the sI and sII phases. 19 The vibrational spectra of C 3 H 8 are presented in Figure 8b.…”

Section: Resultssupporting

confidence: 70%

“…Because of the crucial roles played by NGHs, many experimental and theoretical efforts have been made to study these systems. − Experimentally, Raman, NMR, and other spectroscopic tools are the regular means to study NGHs. Especially, Raman spectroscopy has been used to identify the type of crystal phase, − type of guest molecule, cage occupancy, and hydration number, , to monitor the nucleation and growth processes in real-time, to study phase transformations, , and to detect the location of NGH deposits. , On the basis of Raman spectroscopy measurements, the characteristics of symmetric C–H and C–C stretching vibration of various guest molecules trapped in water cavities of sI, sII, and sH phase have been mapped out, which can be conveniently used to identify the types of crystal phase and guest molecule .…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4] Different crystal phases of hydrates can be formed at appropriate pressure and temperature conditions, such as I, II, H, and some unusual phases (TS-I, 5 HS-I, 6 sK, 7 MH-III, [8][9] and "filled ice" [9][10] ). 1 Six types of polyhedral cavities are included in these phases, shown in Figure 1, which are dodecahedral (D) cavities (5 12 ), irregular dodecahedral (ID) cavities (4 3 5 6 6 3 ), tetrakaidecahedral (T) cavities (5 12 6 2 ), pentakaidecahedral (P) cavities (5 12 6 3 ), hexakaidecahedral (H) cavities (5 12 6 4 ), and icosahedral (I) cavities (5 12 6 8 ), respectively. 1 The detailed structure information of the unit cell of various crystal phases is given in Table 1.…”

Section: Introductionmentioning

confidence: 99%

“…1 Due to the crucial roles played by NGHs, many experimental and theoretical efforts have made to study these systems. [12][13][14][15][16][17][18] Experimentally, Raman, NMR, and other spectroscopic tools are the regular means to study NGHs. Especially, Raman spectroscopy has been used to identify the type of crystal phase, [19][20][21] type of guest molecule, 19 cage occupancy, 21 and hydration number, [21][22] to monitor the nucleation and growth processes in real-time, 23 to study phase transformations, [24][25] and to detect the location of NGH deposits.…”

Section: Introductionmentioning

confidence: 99%

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C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

Liu

Ojamäe

2014

J. Phys. Chem. A

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Abstract:The presence of specific hydrocarbon gas molecules in various types of water cavities in natural gas hydrates (NGHs) are governed by the relative stabilities of these encapsulated guest molecule ─ water cavity combinations. Using molecular quantum-chemical dispersion-corrected hybrid density functional computations, the interaction energies (ΔEhost-guest) and cohesive energies (ΔEcoh), enthalpies and Gibbs free energies for the complexes of host water cages and hydrocarbon guest molecules are calculated at the ωB97X-D/6-311++G(2d,2p) level of theory. The zero point energy effect of ΔEhost-guest and ΔEcoh is found to be quite substantial. The energetically optimal host-guest combinations for seven hydrocarbon gas molecules (CH4, C2H6, C3H6, C3H8, C4H8, i-C4H10, and n-C4H10) and various water cavities (D, ID, T, P, H and I) in NGHs are found to be CH4@D, C2H6@T, C3H6@T, C3H8@T, C4H8@T/P/H, i-C4H10@H, and n-C4H10@H, as the largest cohesive energy magnitudes will be obtained with these host-guest combinations. The stabilities of various water cavities enclosing hydrocarbon molecules are evaluated from the computed cohesive Gibbs free energies: CH4 prefer to be trapped in a ID cage; C2H6 prefer T cages; C3H6 and C3H8 prefer T and H cages; C4H8 and i-C4H10 prefer H cages; and n-C4H10 prefer I cages. The vibrational frequencies and Raman intensities of the C-C stretching vibrational modes for these seven hydrocarbon molecules enclosed in each water cavity are computed. A blue shift results after the guest molecule is trapped from gas phase into various water cages due to the host-guest interactions between the water cage and hydrocarbon molecule. The frequency shifts to the red as the radius of water cages increases. The model calculations support the view that C-C stretching vibrations of hydrocarbon molecules in the water cavities can be used as a tool to identify the types of crystal phases and guest molecules in NGHs.2

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Section: Resultssupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

C–C Stretching Raman Spectra and Stabilities of Hydrocarbon Molecules in Natural Gas Hydrates: A Quantum Chemical Study

Liu

Ojamäe

2014

J. Phys. Chem. A

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“…Moreover, there are too many test steps that take a long time, and do not apply to all methane inclusions. Therefore, previous studies used the Raman scattering peak v 1 of methane inclusions to calculate the density (Seitz et al, 1996;Lin et al, 2007;Lu et al, 2007;Hansen and Berg, 2009). Lu et al (2007) fitted a good linear relationship between the v 1 shift of methane Raman scattering peak and methane density, which is suitable for the density calculation of methane inclusions with methane content of 90%-100%, and the correlation coefficient is 0.9987: where ρ is the density of methane inclusions, g/cm 3 ; D = v 1 − v 0 , v 1 is the measured methane Raman scattering peak of methane inclusions, and v 0 is the methane Raman scattering peak of methane inclusions when the pressure is close to 0.…”

Section: Density Measurement Of Methane Inclusions By Raman Spectroscopymentioning

confidence: 99%

Multi-Phases Fluid Activity Characteristics of Longmaxi Formation and Its Impact on Resistivity in the Changning Area, Southern Sichuan Basin, Southwest China

Cui

Li²,

Han³

et al. 2022

Front. Earth Sci.

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Wells with low gas content and low resistivity in the Changning area, southern Sichuan Basin were selected for this study. The burial-thermal history was reconstructed and the characteristics of multi-phase fluid activity were clarified using microscopic observation and testing of fluid inclusions in the Longmaxi shale fracture veins. Compared with wells with a high gas content and high resistivity, the influence of fluid activity on resistivity was analyzed. The results showed that the thermal evolution of the bituminous inclusions trapped in the veins has reached the stage of carbonaceous-metamorphic bitumen, and the organic matter is fully cracked for gas generation, with some organic matter exhibiting the phenomenon of “graphitization.” The synchronous fluid with bitumen was existed due to shallow burial with a middle-low maturity stage of about 280 and 292 Ma. Two phases of fluids existed in the deep burial stage, thus maturing for about 103 Ma, and the uplift stage at about 28 and 32 Ma, with high homogenization temperatures (Th) (varying from 185 to 195°C and 165–180°C). The corresponding pressure coefficients varied between 1.67 and 2.09, 1.56 and 1.92 in a moderate-strong high-pressure state. The last two phases of fluid formation in the late uplift stage for about 4 to 19 Ma and 6 to 10 Ma were characterized by low salinity at medium-low Th (varied from 140 to 155°C and 120–135°C), with pressures of 57.47–74.50 MPa and 51.44–59.41 MPa (pressure coefficients of 1.09–1.41 and 1.18–1.37), in an atmospheric-weak overpressure state. In the initial uplift stage after deep burial, the fluid closure in the Changning area was good. In contrast, the wells are filled with low gas content because of the strong tectonic forces causing the shale gas to be released and the multi-phase fluid activity that happens during the late uplift stage. New evidence indicates that the emergence of low resistance in the localized Changning area is not only related to the high degree of evolution of organic matter but is also affected by the multi-phase fluid modification in the late uplift stage.

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