[SIO GP Seminars] TODAY: 3:00 PM: Yariv Hamiel, IGPP

[Robin Matoza]

Geophysics Seminar Reminder-

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Friday, January 26, 3:00 PM
   (refreshments served at 2:45 PM)
   Munk Conference Room

													Yariv Hamiel, IGPP

   "Poroelastic damage rheology: dilation, compaction and failure of  
rocks"


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ABSTRACT
A formulation for mechanical modeling of interaction between fracture  
and fluid flow is presented. The model combines the classical Biot's  
poroelastic theory with a damage rheology model. The theoretical  
analysis based on the thermodynamic principles, leads to a system of  
coupled kinetic equations for the evolution of damage and porosity.  
Competition between two thermodynamic forces, one related to porosity  
change and one to microcraking, defines the mode of macroscopic rock  
failure. At low confining pressures rock fails in a brittle mode,  
with strong damage localization in a narrow deformation zone. The  
thermodynamic force related to microcraking is dominant and the yield  
stress increases with confining pressure (positive slope for yield  
curve). The role of porosity related thermodynamic force increases  
with increasing confining pressure, eventually leading to decrease of  
yield stress with confining pressure (negative slope for yield  
curve). At high confining pressures damage is non-localized and the  
macroscopic deformation of the model corresponds to experimentally  
observed cataclastic flow. In addition, the model correctly predicts  
different modes of strain localization such as dilating shear bands  
and compacting shear bands. Numerical simulations in 3D that  
demonstrate rock-sample deformation at different modes of failure are  
also presented. The simulations reproduce the gradual transition from  
brittle fracture to cataclastic flow. The development provides an  
internally consistent framework for simulating coupled evolution of  
fracturing and fluid flow in a variety of practical geological and  
engineering problems such as nucleation of deformation features in  
poroelastic media and fluid flow during seismic cycle.
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