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Seismic Dispersion and Attenuation in Shale Oil Reservoir: Laboratory Experiments and Theoretical Analysis
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  • Zengjia Xiao,
  • Jianguo Zhao,
  • Yanxiao He,
  • Bin Wang,
  • Bohong Yan,
  • Fang Ouyang,
  • Zhi Li
Zengjia Xiao
China University of Petroleum

Corresponding Author:[email protected]

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Jianguo Zhao
China University of Petroleum
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Yanxiao He
China University of Petroleum
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Bin Wang
China University of Petroleum
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Bohong Yan
China University of Petroleum
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Fang Ouyang
China University of Petroleum
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Zhi Li
China University of Petroleum
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Abstract

Different lithofacies of shale oil reservoir invole different lithology(mineral composition), structure(laminated and interbedded crack), pore type and permeability. One of our objectives is to explore the frequency dependent elastic properties and attenuation of the rocks with different lithofacies characteristics for shale oil reservoir. For another significant purpose, we attempt to explain the possible dispersion and attenuation mechanisms in shale using existing theoretical models. We first executed two sets of stress–strain oscillation experiments on partially white-oil saturated samples with different lithofacies, which comes from Inter-Salt shale oil in QianJiang Sag, to investigate the dispersion of elastic moduli, elastic and anelastic parameters, anisotropy and attenuation from seismic to ultrasonic frequencies. Assuming that the formation conforms to the characteristics of VTI medium, the experiments were carried out at a confining pressure range between 5 and 30MPa in the frequency range 1 to 1000Hz using two samples drilled in vertical and parallel directions to the formation bedding. And then we not only evaluate the applicability of the anisotropic Gassmann theory to the Inter-Salt shale, but also discuss the experimental phenomenon at mesoscopic and microscopic scales. The results of our broad-frequency experiment study illustrated that the dispersion and attenuation for compression/extension vertical to bedding is larger than that parallel to bedding in partial fluid saturation, and exhibiting different attenuation characteristic peaks. The increase of shear stiffness tensor with frequency seems to indicate the inapplicability of anisotropic Gassmann theory. The interpretation of the attenuation measurements in terms of well-established theoretical models which depict the wave-induced flow of pore fluid at the mesoscopic scale was discussed in terms of the Lithofacies characteristics, include intergranular pores and horizontal interlayer fractures,et al.