[CIG-SHORT] pseudo plane-strain in Pylith

[Lucas Abraham Willemsen]

Hello,

Currently I am trying to investigate the geomechanical response of a reservoir with a single fault when CO2 is injected. The fluid-flow part of the problem is performed by a code which is coupled to Pylith. The results from Pylith are fed into the flow code, which marches time forward and the  new fluid pressures are then fed back into Pylith, etc.

The CO2 sequestration geometry I am considering is plane-strain, but the complication is that the flow-code (currently experimental) only works with hexahedrals. So I turned the 2D problem into a 3D-problem that is 1-element thick in the out-of-plane direction (y-direction). To enforce plane strain conditions I put zero displacement in the y-direction on the front and back plane. But the problem is that the fault intersects these front and back planes. This is a natural consequence of turning the 2D geometry with fault into a 1-element thick 3D geometry with fault.

All of the input parameters are independent of 'y' since I am trying to model a plane strain problem. So there should be no reason for slip in the y-direction on any of the fault nodes (intuitively speaking). But Pylith does not allow me to explicitly constrain the y-displacements of the fault where they intersect the front and back plane. Therefore, the only way to run the model is by excluding the nodes on the fault from the front- and back- plane nodesets. But this way the boundary condition on these fault nodes is effectively zero normal stress, and elastic extrusion of material takes places. (Applying Neumann B.C. with normal stress to these fault nodes on the front and back plane to somehow reduce the extrusion does not seem to affect the fault nodes either. It would not be a great solution anyway).

Is there a way to deal with faults in this 'pseudo plane-strain' geometry I described?

sincerely,
Lucas
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://geodynamics.org/pipermail/cig-short/attachments/20130405/f678922f/attachment.htm