Experimental and theoretical study of frequency and temperature dependence on seismic attenuation of saturated rocks

摘要

Most rocks are saturated or partly saturated with different fluids under different depth, temperature and pressure conditions. It is generally acknowledged that fluids have the most important effect on the attenuation and dispersion of seismic waves. There exists a relation between frequency- and temperature- dependence on rock's seismic properties. It is not yet clear in literature whether there exist other equally important attenuation mechanisms as that in Biot's model, since there are other sources of dissipation, also related to fluids, that are not considered in Biot theory but that may also contribute to the overall dissipation of seismic energy. Identifying the precise relaxation mechanisms is still the subject of experimental and theoretical research. In this article, a series of experiments are conducted on dry and saturated rocks (sandstone, marble, granite) at different temperatures and frequencies to find the attenuation mechanism of interaction between rock skeleton and pore-fluid. Fluid viscosity generally depends on temperature, so the effect of pore fluid on attenuation is confirmed in terms of apparent viscosity variation of rock caused by the change of pore-fluid conditions (such as frequency or temperature). Based on our experimental data, we develop a new model of macroscopic apparent viscosity in saturated rock which is consistent with the nonlinear relaxation law. It helps to derive the analytical expressions to compute velocity dispersion and attenuation as functions of frequency and temperature.