Mechanics of stratified anisotropic poroelastic media |
Undrained boundary conditions place the hard constraint on the fluid increment , requiring no flow at the boundaries, so at all boundaries. These conditions ensure that the fluid pressure does change, since as the boundaries move in or out the pressure on the confined fluid is increasing or decreasing.
Both of these conditions must be approximations to conditions in a generally realistic earth model. It is easy to imagine situations where some boundaries between layers (the vertical direction) are plugged, so undrained boundary conditions might be correct while neighboring layers (horizontal direction) might be open to fluid flow (so and/or ). I will consider these more general situations in later work, but for now limit the analysis to that for either all drained conditions or all undrained conditions. All undrained conditions are also appropriate, as mentioned previously, regardless of the physical boundary conditions if the probe changing the physical variables is a passing high frequency acoustic or seismic wave train or pulse.
Mechanics of stratified anisotropic poroelastic media |