The Evolution of
Fracturing and Related Permeability Patterns in Numerical-Analytical Models
(FRAPtre) of Fault
Zone Growth
Salvini, Francesco, Fabrizio Balsamo, Fabrizio Storti, Università degli Studi Roma Tre, Rome, Italy
The interaction
of many parameters controls the evolution of deformational architectures during
faulting, including the fault
geometry and kinematics, the
fault
slip
mechanism, the amount of
fault
displacement, the rock type and rheology, the
boundary stress conditions, the pore fluid pressure, and the structural
inheritance. Substantial improvements of our predictive capability of fracture
distributions in hydrocarbon exploration and development require to implement
these parameters in modelling tools. We developed a numerical-ana-lytical tool
(FRAPtre) that links these parameters to the deformation pattern for a given
fault
geometry and kinematics. Results include also the static stress
conditions evaluation as well as the permeability prediction. The
fault
surfaces are gridded and stress/strength conditions at each cell are
analytically computed by a series of stress tensor additions. The strength
values are then computed by projecting the resulting stress tensor on the
fault
cell surfaces, as well as the normal pressure and the shear. These parameters
allow to compute the deformation function DF i.e. the difference between shear
and strength on the
fault
cell surface. DF measures the disposition of rock to
break into a cataclastic fabric and then to form gouge layers. The
Fault
Gouge
Index FGI is computed by cumulating the deformation function of all cells along
the displacement path and multiplied by the clay content fraction at that cell.
Finally,
fault
permeability is computed by a generalised equation that matches
fault
core permeability values available in the literature. Application to
natural examples validates the proposed numerical-analytical approach.