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SCIENCE CHINA Earth Sciences, Volume 61 , Issue 9 : 1261-1278(2018) https://doi.org/10.1007/s11430-017-9214-2

Seismic rock physical modelling for gas hydrate-bearing sediments

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  • ReceivedSep 11, 2017
  • AcceptedApr 16, 2018
  • PublishedJul 10, 2018

Abstract


Funded by

the National Natural Science Foundation of China(Grant,No.,41706042)

the China Postdoctoral Science Foundation(Grant,No.,2015M582060)

the Special Research Grant for Non- profit Public Service(Grant,No.,201511037)

the National key research and development program(Grant,No.,2017YFC0307400)

the foundation of Key Laboratory of Submarine Geosciences(Grant,No.,KLSG1603)


Acknowledgment

This study was supported by the National Natural Science Foundation of China (Grant No. 41706042), the China Postdoctoral Science Foundation (Grant No. 2015M582060), the Special Fund for Land & Resources Scientific Research in the Public Interest (Grant No. 201511037), the National Key Research and Development Program (Grant No. 2017YFC0307400) and the Foundation of Key Laboratory of Submarine Geosciences (Grant No. KLSG1603).


References

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  • Figure 1

    CT imagery and diagrams for the micro-distribution of gas hydrates. (a) X-ray Micro CT imagery in a laboratory-made sample (modified from Jin et al., 2006), we can see sand grains (white), gas (black), water (light grey) and hydrate (yellow, which is represented by GH in the figure); (b) configuration for pore-filling gas hydrates; (c) configuration for load-bearing gas hydrates.

  • Figure 2

    Diagram of the rock physical modelling method. The diagram in the left red box shows the rock physical modelling method for load-bearing gas hydrate-bearing sediments, and the diagram in the right blue box shows the rock physical modelling method for pore-filling gas hydrate-bearing sediments.

  • Figure 3

    Velocities and VP/VS versus gas hydrate saturation for gas hydrate-bearing sediments. (a) VP; (b) VS; (c) VP/VS. ϕ represents porosity of gas hydrate-bearing sediments.

  • Figure 4

    Velocities versus hydrate saturation for gas hydrate-bearing sediments with different PARs of penny-shaped pores. (a) VP; (b) VS; (c) VP/VS.

  • Figure 5

    Velocities versus hydrate saturation for gas hydrate-bearing sediments with different PARs of ellipsoidal pores. (a) VP; (b) VS; (c) VP/VS.

  • Figure 6

    Velocities and VP/VS versus gas saturation at different gas saturations. (a) VP; (b) VS; (c) VP/VS.

  • Figure 7

    Elastic moduli, velocities and VP/VS versus shear modulus of hydrate at different hydrate saturations. (a) Bulk modulus; (b) shear modulus; (c) VP; (d) VS; (e) VP/VS.

  • Figure 8

    Crossplots of elastic parameters. (a) Crossplot of λρ and μρ for PFGH formation; (b) crossplot of λρ and μρ for LBGH formation; (c) crossplot of Poisson’s ratio and Russell fluid factor for PFGH formation; (d) crossplot of Poisson’s ratio and Russell fluid factor for LBGH formation. ϕ is sediment porosity, and the colour bars to the rights of the crossplots represent hydrate saturation.

  • Figure 9

    Indictor of elastic parameters for hydrate saturation. (a) λρ; (b) μρ; (c) poisson’s ratio; (d) russell fluid factor. The four bars corresponding to each hydrate saturation value from left to right represents PFGH formations with 10% porosity, LBGH formations with 10% porosity, PFGH formations with 40% porosity and LBGH formations with 40% porosity, respectively.

  • Figure 10

    Properties and experimental results for thirteen specimens. (a) Hydrate saturation and porosity; (b) measured velocities with an effective confining pressure of 500 kPa. The P-wave velocity and S-wave velocity are measured when pore-filling materials are hydrate and free gas (dry specimens), and water saturated P-wave velocity is calculated after gas-water substitution.

  • Figure 11

    PAR inverted from the measured velocities for thirteen specimens. The blue and red bars represent the PARs inverted for the measured P-wave and S-wave velocities, respectively.

  • Figure 12

    Calculated results for thirteen sand specimens. (a) Water-saturated VP and VS; (b) water-saturated VP/VS; (c) inversed hydrate saturation from calculated VP and VS.

  • Figure 13

    Measured well log data at site SH2. The well log curves rom left to right are gamma ray, acoustic travel-time, borehole diameter, density, resistivity, and neutron logging. The dotted green box represents the hydrate layer.

  • Figure 14

    Calculated porosity and pore aspect ratios. (a) Porosity calculated from density; (b) aspect ratio of ellipsoidal pores; (c) aspect ratio of penny-shaped pores.

  • Figure 15

    Calculated velocities, Poisson’s ratio and hydrate saturation for the gas hydrate-bearing layer at site SH2. (a) VP, the red solid line represents the measured values, and the blue solid line represents the calculated values; (b) calculated VS; (c) Poisson’s ratio, the red solid line represents the values calculated by the measured VP and calculated VS, and the blue solid line represents the values calculated by the calculated VP and VS; (d) hydrate saturation, the red solid line represents the hydrate saturation calculated using the Archie equation, and the blue solid line represents the hydrate saturation inverted from the calculated VS.

  • Figure 16

    Relative errors of the calculated and measured values of P-wave velocity.

  • Figure 17

    Crossplots of elastic parameters for gas hydrate-bearing sediments at site SH2. (a) Crossplot of measured VP and Gamma; (b) crossplot of VP and Poisson’s ratio; (c) crossplot of λρ and μρ. The colorbars on the right of each crossplot represent hydrate saturation.

  • Table 1   Elastic constants of sediment constituents

    Component

    Bulk modulus (GPa)

    Shear modulus (GPa)

    Density (g cm−3)

    Sources

    Quartz

    37.0

    44.0

    2.65

    Carmichael, 1989

    Clay

    21.0

    7.0

    2.60

    Tosaya and Nur, 1982

    Gas hydrate

    7.7

    3.2

    0.91

    Waite et al., 2000

    Water

    2.25

    1000

     

    Gas

    0.00013

    0.65

     

  • Table 2   Most cited elastic constants of gas hydrates

    Bulk modulus (GPa)

    Shear modulus (GPa)

    Density (g cm−3)

    Sources

    Work area

    5.6

    2.4

    0.767

    Ecker, 2001

    Blake Outer Ridge

    6.41

    2.54

    0.91

    Lee and Collett, 2001

    Mallik 2L-38 well

    7.7

    3.2

    0.91

    Waite et al., 2000

    laboratory experiments

    7.9

    3.3

    0.9

    Helgerud et al., 1999

    ODP164, Site 995

    8.7

    3.5

    0.92

    Shankar and Riedel, 2011

    Krishna-Godavari basin

    8.41

    3.54

    0.925

    Helgerud et al., 2009

    laboratory experiments

  • Table 3   Elastic moduli and densities of minerals for site SH2

    Components

    Bulk modulus (GPa)

    Shear modulus (GPa)

    Density (kg m−3)

    Methane hydrate (5 MPa, 273 K)

    8.41

    3.54

    0.922

    Methane gas (10 MPa, 273 K)

    0.015

    0

    90

    Mineral mixture

    45.27

    26.0

    2.667

    Data sources: Wang et al., 2011

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