In hydrate-bearing sediments, the elastic wave attenuation characteristics depend on the elastic properties of the sediments themselves on the one hand, and on the other hand, they also depend on the hydrate occurrence state and hydrate saturation. Since the hydrate-bearing sediments always have high porosity, so they show significant porous medium characteristics. Based on the BISQ porous medium model which is the most widely used model to study the attenuation characteristics in the porous media, we focused on p-wave attenuation in hydrate-bearing sediments in Shenhu Area, South China Sea, especially in specific seismic frequency range, which lays a foundation for the identification of gas hydrates by using seismic wave attenuation in Shenhu Area, South China Sea. Our results depict that seismic wave attenuation is an effective attribute to identify gas hydrates. 1. Introduction With the enhancement of exploration technology for gas hydrate resources, research on wave attenuation in hydrate-bearing sediments is being paid more and more attention. Unlike oil and gas reservoirs, hydrate reservoirs are usually found at shallow depths. In suitable conditions, hydrates form more easily within sediments with high porosity and high permeability. Gas hydrates affect the rock properties, so the wave attenuation in hydrate-bearing sediments is a complex phenomenon. In Mackenzie Delta, Canada, Guerin and Goldberg [1], Guerin et al. [2], and Pratt et al. [3] obtained high value of wave attenuation in hydrate-bearing sediments by logging data and crosshole seismic tomography results, respectively. In Nankai Trough, central Japan, Matsushima [4] also proved that elastic wave showed strong attenuation in hydrate-bearing sediments by logging data, in Blake Ridge and in the Makran Accretionary Prism, Arabian Sea, Wood et al. [5] and Sain and Singh [6] obtained week attenuation of seismic wave in hydrate-bearing sediments by using seismic data. Although the wave attenuation mechanism in hydrate-bearing sediments is not yet well explained. But the existing research results show that the wave attenuation in hydrate-bearing sediments is associated with several factors, such as the elastic properties of sediments, hydrate occurrence state, hydrate saturation, and frequency. Since the hydrate-bearing sediments always have high porosity, so they show significant porous medium characteristics. At the present, the most commonly used model to study elastic wave propagation in porous media is the BISQ model which combines the Biot flow and the squirt flow. In this model, the
References
[1]
G. Guerin and D. Goldberg, “Sonic waveform attenuation in gas hydrate-bearing sediments from the Mallik 2L-38 research well, Mackenzie Delta, Canada,” Journal of Geophysical Research B, vol. 107, no. 5, pp. EPM 1-1–EPM 1-11, 2002.
[2]
G. Guerin, D. Goldberg, T. S. Collett, and Sonic attenuation in the JAPEX/JNOC/GSC, “Mallik 5L-38 gas hydrate production research well,” in Scientific Results From the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, S. R. Dallimore and T. S. Collett, Eds., Bulletin 585, pp. 1–14, Geological Survey of Canada, 2005.
[3]
R. G. Pratt, F. Hou, K. Bauer, et al., “Waveform tomography images of velocity and inelastic attenuation from the Mallik 2002 crosshole seismic surveys,” in Scientific Results From the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, S. R. Dallimore and T. S. Collett, Eds., Bulletin 585, pp. 1–14, Geological Survey of Canada, 2005.
[4]
J. Matsushima, “Attenuation measurements from sonic full waveform logs in gas hydrate bearing sediments,” in Proceedings of the of 74th SEG Annual International Meeting, pp. 346–349, 2004.
[5]
W. T. Wood, W. S. Holbrook, and H. Hoskins, “In situ measurements of P-wave attenuation in the methane hydrate- and gas-bearing sediments of the Blake Ridge,” Proceedings of the Ocean Drilling Program: Scientific Results, vol. 164, pp. 265–272, 2000.
[6]
K. Sain and A. K. Singh, “Seismic quality factors across a bottom simulating reflector in the Makran Accretionary Prism, Arabian Sea,” Marine and Petroleum Geology, vol. 28, no. 10, pp. 1838–1843, 2011.
[7]
J. Dvorkin and A. Nur, “Dynamic poroelasticity: a unified model with the squirt and the biot mechanisms,” Geophysics, vol. 58, no. 4, pp. 524–533, 1993.
[8]
J. Dvorkin, R. Nolen-Hoeksema, and A. Nur, “The squirt-flow mechanism: macroscopic description,” Geophysics, vol. 59, no. 3, pp. 428–438, 1994.
[9]
G. Mavko, T. Mukerji, and J. Dvorkin, The Rock Physics Handbook, Cambridge University Press, 1998.
[10]
R. Hill, “The elastic behaviour of a crystalline aggregate,” Proceedings of the Physical Society A, vol. 65, pp. 349–354, 1952.
[11]
J. Dvorkin, M. Prasad, A. Sakai, and D. Lavoie, “Elasticity of marine sediments: rock physics modeling,” Geophysical Research Letters, vol. 26, no. 12, pp. 1781–1784, 1999.
[12]
A. Nur, G. Mavko, J. Dvorkin, et al., “Critical porosity: the key to relating physical properties to porosityin rocks,” in Proceedings of the 65th SEG Annual International Meeting, pp. 878–882, 1995.
[13]
J. Dvorkin and A. Nur, “Elasticity of high-porosity sandstones: theory for two north sea data sets,” Geophysics, vol. 61, no. 5, pp. 1363–1370, 1996.
[14]
R. D. Mindlin, “Compliance of elastic bodies in contact,” Journal of Applied Mechanics, vol. 16, pp. 259–268, 1949.
