Effects of pressure on pore characteristics and permeability of porous rocks as estimated from seismic wave velocities in cores from TCDP Hole-A
Journal
Geophysical Journal International
Journal Volume
182
Journal Issue
3
Pages
1148-1160
Date Issued
2010
Author(s)
Kitamura, Keigo
Takahashi, Miki
Mizoguchi, Kazuo
Masuda, Koji
Ito, Hisao
Abstract
Changes in V p /V s (Poisson's ratio) around a fault are related to changes in the fluid transport properties of rocks, which play a significant role in seismogenic processes. Here we report a notable relationship between V p /V s and the permeability of porous fault-related rocks (Chelungpu fault, Taiwan) by direct and simultaneous measurement of elastic wave velocities (V p and V s ) and permeability under increasing effective confining pressure (P eff ) up to 25 MPa. V p and V s for all samples increased with P eff in the range up to 20 MPa, then were nearly constant as P eff increased to 25 MPa. Most silty sandstones with large proportions of fine-grained material showed positive correlations between V p /V s and permeability with rising pressure. On the other hand, well-sorted sandstones showed only slight changes in permeability with respect to V p /V s with rising pressure. We infer that grain size distributions, in particular the amount of silt-and clay-size grains, are responsible for the change in permeability with pressure as small particles clog pore networks with increasing P eff , causing the decrease in permeability. These findings may be useful to explain changes in permeability and pore pressure in the deep crust.
Type
journal article