Abstract：It is known that viscous and inertial coupling between the frame of a porous rock and its pore fluid dissipates seismic energy by conversion to heat and hence will cause attenuation. Cole-Cole distribution modified Debye model is always used to explain the internal friction of rock. However，this model is suitable only for homogeneous medium，not quite suitable for complex fluid saturated porous rock medium. Obviously，internal friction experimental data under low frequency condition are not coincident with Cole-Cole distribution modified Debye model. Their Re-Im modulus curves do not have the common “arc-shaped” features represented by Debye model. It is suggested that the behaviours of Re-Im modulus curves can be explained by permeability scale effect in wave-induced fluid relaxation of porous rock medium，which is necessary to be extension to Cole-Cole distribution modified Debye model. Internal friction experimental data show that all the Im-Re curves are alike，with same asymmetric arc-shaped form in both high and low temperature. Especially in low temperature，the curves separate and ascend，and ascend more acutely as the frequency increases. Thats a certain evidence of permeability scale effect in fluid relaxation of heterogeneous rocks with micro-cracks. It can be used to improve methods of geological interpretation of acoustical and seismic data and helps to improve the model containing relaxation mechanism of saturated rocks，and to explain the relevant experimental data reasonably. Based on research of predictive model of the relaxation behaviours of fluid saturated rocks，multi-scale structural information about the heterogeneous rocks may be picked up from the experimental data.
