  Large scale modelling of fluid flow coupled with solid failure in geothermal
reservoirs or hydrocarbon extraction from reservoir rocks usually involves
behaviours at two scales: lower scale of the inelastic localization zone, and
larger scale of the bulk continuum where elastic behaviour can be reasonably
assumed. The hydraulic conductivities corresponding to the mechanical
properties at these two scales are different. In the bulk elastic host rock,
the hydraulic conductivity does not vary much with the deformation, while it
significantly changes in the lower scale of the localization zone due to
inelastic deformation. Increase of permeability due to fracture and/or
dilation, or reduction of permeability due to material compaction can take
place inside this zone. The challenge is to predict the evolution of hydraulic
conductivities coupled with the mechanical behaviour of the material in all
stages of the deformation process. In the early stage of diffuse deformation,
the permeability of the material can be reasonably assumed to be homogenous
over the whole Representative Volume Element (RVE) However, localized failure
results in distinctly different conductivities in different parts of the RVE.
This paper establishes a general framework and corresponding field equations to
describe the hydro-mechanical coupling in both diffuse and localized stages of
deformation in rocks. In particular, embedding the lower scale hydro-mechanical
behaviour of the localization zone inside an elastic bulk, together with their
corresponding effective sizes, helps effectively deal with scaling issues in
large-scale modelling. Preliminary results are presented which demonstrate the
promising features of this new approach.

Soft Condensed Matter