Permeability from seismic

Permeability from seismic refers to the idea that one can estimate a rock's permeability by performing a seismic experiment and analyzing the rock's seismic response.

Theory

In Biot theory, as a P-wave propagates through a rock, a pressure gradient will develop from an area of dilation to one of compression. The fluids in the pores will try to move from the areas of compression to those of dilation along these pressure gradients, in what is referred to as squirt flow. If the fluids are allowed to move (i.e. high permeability), the rock will be more easily compressed, and its apparent velocity will be lower. If they are not able to move (i.e. low permeability), the fluids will help the rock resist the compression and provide a higher overall apparent velocity.

The frequency of the P-wave plays an important role in this phenomenon. If the frequency of the wave is too high, the fluids will not have time to move from the compression areas to the dilation areas before the locations of these areas change. Therefore, at high enough frequencies, the rock will have a low apparent permeability (regardless of its true permeability) and fluids will stay within the compressed pores resisting the compression. However, at low frequencies, fluids will flow from compressed pores to dilated ones unless the rock truly has low permeability.