期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
卷 121, 期 3, 页码 1664-1676出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015JB012575
关键词
attenuation
资金
- Swiss National Science Foundation
Using the forced oscillation method, we measure the extensional-mode attenuation and Young's modulus of a Berea sandstone sample at seismic frequencies (0.5-50Hz) for varying levels of water saturation (similar to 0-100%) and confining pressures (2-25MPa). Attenuation is negligible for dry conditions and saturation levels <80%. For saturation levels between similar to 91% and similar to 100%, attenuation is significant and frequency dependent in the form of distinct bell-shaped curves having their maxima between 1 and 20Hz. Increasing saturation causes an increase of the overall attenuation magnitude and a shift of its peak to lower frequencies. On the other hand, increasing the confining pressure causes a reduction in the attenuation magnitude and a shift of its peak to higher frequencies. For saturation levels above similar to 98%, the fluid pressure increases with increasing confining pressure. When the fluid pressure is high enough to ensure full water saturation of the sample, attenuation becomes negligible. A second series of comparable experiments reproduces these results satisfactorily. Based on a qualitative analysis of the data, the frequency-dependent attenuation meets the theoretical predictions of mesoscopic wave-induced fluid flow (WIFF) in response to a heterogeneous water distribution in the pore space, so-called patchy saturation. These results show that mesoscopic WIFF can be an important source of seismic attenuation at reservoir conditions.
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