Polygonal faults are non-tectonic fault systems which are layer-bound (at some
vertical scale) and are widely developed in fine-grained sedimentary basins.
Although several qualitative mechanisms have been hypothesised to explain the
formation of these faults, there is a weak general consensus that they are
formed by the coupled deformation and fluid expulsion of the host sediments
(consolidation). This thesis presents a numerical framework that can be
extended to investigate the role consolidation plays in the development and
evolution of these faults.
The method is also applicable to reservoir engineering and CO2 storage. An
understanding of the coupled mechanical response and fluid flow is critical in
determining compaction and subsidence in oil reservoirs and fault-seal
integrity during CO2 disposal and storage.
The technique uses a fracture mapping approach (FM) and the extended
finite element method (XFEM) to modify the single phase FEM consolidation
formulation. A key feature of FM-XFEM is its ability to include discontinuities
into a model independently of the computational mesh.
The fracture mapping approach is used to simulate the flow interaction
between the matrix and existing fractures via a transfer function. Since
fractures are represented using level set data, the need for complex meshing to
describe fractures is not required.
The XFEM component of the method simulates the influence of the pore
fluid on the mechanical behaviour of the fractured medium. In XFEM,
enrichment functions are added to the standard finite element approximation
to ensure an accurate approximation of discontinuous fields within the
simulation domain.
FM-XFEM produces results comparative to the discrete fracture method on
relatively coarse meshes. FM-XFEM has also been extended to model the
propagation of existing fractures using a mixed-mode criterion applicable to
geological media. Stress concentrations at the tips of existing fractures show
good agreement with an analytical solution found in literature.