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A Comparison of Seismic Attenuation Models for Unconsolidated Surficial Sediments: Evidence from Multi-Frequency Sonic Logs
The attenuation of seismic waves is an important material parameter which contains potentially valuable information on key properties of the probed medium. An inherent complication arising in the interpretation of such measurements is, however, that there are multiple physical mechanisms contributing to the dissipation of seismic energy, such as wave-induced fluid flow at the micro-, meso-, and macroscopic scales. In addition to this, the relative contribution and importance of the various mechanisms are generally unknown and difficult to unravel. To address this problem for the practically relevant case of unconsolidated surficial sediments, we analyze multi-frequency sonic logs with dominant source frequencies ranging between 1 and 30 kHz. In order to estimate appropriate corrections for near-field and geometrical spreading effects, which are essential to obtain reliable estimations of attenuation, we model our experimental setup using a numerical solution of the poro-elastic equations in cylindrical coordinates. After having applied the thus inferred corrections, this broadband dataset, in conjunction with a comprehensive suite of complementary logging data, allows for building a realistic rock physics model. This, in turn, provides the basis for simulating the various seismic attenuation mechanisms and for assessing their relative importance. We demonstrate that, while the levels of attenuation due to the presence of mesoscopic heterogeneities expected for the considered case are negligible, the energy losses produced by fluid flow at microscopic and macroscopic scales can be very significant. Results based on Monte-Carlo-type inversions indicate that the Biot's intrinsic macroscopic attenuation allows for obtaining a good representation of most of the data, while refinements provided by including microscopic loss are locally meaningful.
A Comparison of Seismic Attenuation Models for Unconsolidated Surficial Sediments: Evidence from Multi-Frequency Sonic Logs
The attenuation of seismic waves is an important material parameter which contains potentially valuable information on key properties of the probed medium. An inherent complication arising in the interpretation of such measurements is, however, that there are multiple physical mechanisms contributing to the dissipation of seismic energy, such as wave-induced fluid flow at the micro-, meso-, and macroscopic scales. In addition to this, the relative contribution and importance of the various mechanisms are generally unknown and difficult to unravel. To address this problem for the practically relevant case of unconsolidated surficial sediments, we analyze multi-frequency sonic logs with dominant source frequencies ranging between 1 and 30 kHz. In order to estimate appropriate corrections for near-field and geometrical spreading effects, which are essential to obtain reliable estimations of attenuation, we model our experimental setup using a numerical solution of the poro-elastic equations in cylindrical coordinates. After having applied the thus inferred corrections, this broadband dataset, in conjunction with a comprehensive suite of complementary logging data, allows for building a realistic rock physics model. This, in turn, provides the basis for simulating the various seismic attenuation mechanisms and for assessing their relative importance. We demonstrate that, while the levels of attenuation due to the presence of mesoscopic heterogeneities expected for the considered case are negligible, the energy losses produced by fluid flow at microscopic and macroscopic scales can be very significant. Results based on Monte-Carlo-type inversions indicate that the Biot's intrinsic macroscopic attenuation allows for obtaining a good representation of most of the data, while refinements provided by including microscopic loss are locally meaningful.
A Comparison of Seismic Attenuation Models for Unconsolidated Surficial Sediments: Evidence from Multi-Frequency Sonic Logs
Milani, Marco (author) / Rubino, J. Germán (author) / Baron, Ludovic (author) / Sidler, Rolf (author) / Holliger, Klaus (author)
Fifth Biot Conference on Poromechanics ; 2013 ; Vienna, Austria
Poromechanics V ; 239-248
2013-06-18
Conference paper
Electronic Resource
English
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