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Seismic Characteristics in Marine Hydrate Systems

This study investigates the seismic characteristics of gas hydrates in marine sediments and their potential as an energy resource. The findings highlight the use of seismic techniques for identifying hydrates and the influence of hydrate accumulation on seismic blanking and reflection.

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Seismic Characteristics in Marine Hydrate Systems

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  1. Seismic Characteristics in Marine Hydrate Systems Guangsheng Gu1Advisors: George J. Hirasaki1, Walter G. Chapman1Collaborators:Colin A. Zelt2, Priyank Jaiswal21 Dept. of Chemical & Biomolecular Engineering2 Dept. of Earth ScienceRice University, Houston, TX, 77005 Consortium on Processes in Porous Media, 15th, April 26, 2011 Rice University, Houston

  2. What is Gas Hydrate • Crystalline compounds, with gas molecules (e.g. CH4, C2H6) captured in water molecular cages • Dissociation: 1m3 methane hydrate = 168 m3 CH4 + 0.8 m3 H2O • Stable at high pressure and low temperature, typically in deep marine sediments or in permafrost environments

  3. Why Study Hydrates? Geohazards -Submarine slope failure Influence on global climate change World-wide distribution; huge potential amount, as energy resource T.S. Collett, Offshore Technol. Conf. (OTC) 2008.

  4. Major Seismic Characteristics • Used to identify hydrates in marine sediments • Bottom Simulating Reflector (BSR) • Seismic Blanking in Lateral Strata • Wipeout in Gas Chimeny

  5. Bottom Simulating Reflector (BSR) • A strong reflector below seafloor • Parallel to the seafloor • Indicating the abrupt transition from hydrate to free gas phase below • In good accordance with 3-phase equilibrium of a pure-methane system Hydrate or Gas Saturation Abrupt Change Taylor et al., 1992; M.W. Lee et al, 2001

  6. Seismic Blanking inLateral Strata Hydrate accumulation induces blanking

  7. Seismic Blanking MJ. Hornbach, WS. Holbrook, et al., Geophysics, v. 68, n. 1, 92–100,2003.

  8. Seismic Blanking Weak reflection in seismic profiling: R < RBSR/10 Typically R < 0.02

  9. Geologic Setting In Reflection Layer 1 Layer 2 (shale/clay) Reflection Coefficient: Transmission Coefficient:

  10. Estimation of Acoustic Properties Average P-wave Velocity: Revised from the Time-average Equation (Pearson et al., 1983). Average Density: phase i =w,H,V 10

  11. Intrinsic Properties of Phases Table 1: Acoustic properties of components Acoustic velocities from W.J. Winters and W.F. Waite (2007); Sloan (2007), etc.. Nick Barton, Rock Quality, Seismic Velocity, Attenuation and anisotropy, Taylor & % Francis Group, 2007, p. 12. Table 2: Porosity and saturation ranges 11 The ranges of porosity were obtained from Hirasaki (lecture note, 2006), Jenyon (2006), Magara (1980).

  12. (Case 1) Impossible to be blanking Blanking Range

  13. (Case 2) Possible to be blanking Blanking Range

  14. (Case 3 ) Impossible to be blanking Blanking Range

  15. Just possible to be blanking Reflection Coeffiecient Blanking region Sh in sand layer

  16. Very possible to be blanking Reflection Coeffiecient Blanking region

  17. Just Possible to be blanking Reflection Coeffiecient Blanking region

  18. Different Layer (Diatomite vs. Clay) Very possible to be blanking Blanking region

  19. Conclusion • Hydrate accumulation in marine sediment is helpful for blanking; • Sensitive to parameters and stratum lithology; • Hydrate accumulation doesn’t guarantee a blanking.

  20. Wipeout in gas chimney KIGAM data showing BSR in debris-flow deposits (DFD). BSR is weak and discontinuous. Seismic chimneys look very narrow due to vertical exaggeration (ca. 14×). Seismic chimney, marked by S, is about 820 m wide and 110 m tall above the BSR, forming a rather horizontal zone of amplitude reduction. DFD, debris-flow deposits; THS, turbidite/hemipelagic sediments. Wipe out in vertical columnar regions S. Horozal et al., Marine Geology 258: 126–138, 2009.

  21. gas chimney Northern Cascadia margin near Ocean Drilling Program (ODP) Site 889/890. Geological Society of America Bulletin, Riedel, 2006.

  22. Riedel, 2006.

  23. chimney S. Horozal et al., Marine Geology 258: 126–138, 2009.

  24. Mechanisms Due to gas bubbles in the GHSZ in the Cascadia Margin (Wood et al., 2002). These gas bubbles may be coated with hydrate that prevents the inflow of water (Riedel et al., 2006). Due to a thermal (Wood et al., 2002) or a thermo-chemical effects (Hornbach et al., 2005) Due to presence of gas hydrate, and intrinsic acoustic properties in sediments (Chand and Minshull, 2003.).

  25. Acknowledgement • DOE Grant (No. DE-FC26-06NT42960) • Rice University, Hirasaki Group, Chapman Group • Colleagues in Earth Science Department

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