Numerical analysis of seismic wave propagation in fluid-saturated porous multifractured media
Guo Gui-Hong1, Yan Jian-Ping2, Zhang Zhi3, José Badal4, Cheng Jian-Wu5, Shi Shuang-Hu6, and Ma Ya-Wei1
1. Lanzhou University & The Key Laboratory of Mechanics on Disaster and Environmental in Western China, Lanzhou 730000, China.
2. Lanzhou University & School of Earth Sciences, Lanzhou 730000, China.
3. School of Earth Science, Guilin university of science and technology, Guilin 541004, China.
4. Physics of the Earth, Sciences B, University of Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain.
5. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China.
6. BGP International, CNPC, Zhuozhou 072751, China.
Abstract Elastic wave propagation and attenuation in porous rock layers with oriented sets of fractures, especially in carbonate reservoirs, are anisotropic owing to fracture sealing, fracture size, fracture density, filling fluid, and fracture strike orientation. To address this problem, we adopt the Chapman effective medium model and carry out numerical experiments to assess the variation in P-wave velocity and attenuation, and the shear-wave splitting anisotropy with the frequency and azimuth of the incident wave. The results suggest that velocity, attenuation, and anisotropy vary as function of azimuth and frequency. The azimuths of the minimum attenuation and maximum P-wave velocity are nearly coincident with the average strike of the two sets of open fractures. P-wave velocity is greater in sealed fractures than open fractures, whereas the attenuation of energy and anisotropy is stronger in open fractures than sealed fractures. For fractures of different sizes, the maximum velocity together with the minimum attenuation correspond to the average orientation of the fracture sets. Small fractures affect the wave propagation less. Azimuth-dependent anisotropy is low and varies more than the other attributes. Fracture density strongly affects the P-wave velocity, attenuation, and shear-wave anisotropy. The attenuation is more sensitive to the variation of fracture size than that of velocity and anisotropy. In the seismic frequency band, the effect of oil and gas saturation on attenuation is very different from that for brine saturation and varies weakly over azimuth. It is demonstrated that for two sets of fractures with the same density, the fast shear-wave polarization angle is almost linearly related with the orientation of one of the fracture sets.
This study was supported by the National Natural Science Foundation of China Rsearch (Nos. 41674046, 41440030, and 41574078) and the Fundamental Research Funds for the Central Universities of Lanzhou university (No. lzujbky-2015-175).
Cite this article:
. Numerical analysis of seismic wave propagation in fluid-saturated porous multifractured media[J]. APPLIED GEOPHYSICS, 2018, 15(2): 311-317.
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