Micromechanics of Cataclastic Pore Collapse in Porous Limestone

The analysis of compactant failure in carbonate formations hinges upon a fundamental understanding of the mechanics of inelastic compaction. We present new microstructural observations on micritic and allochemical limestones deformed under hydrostatic and triaxial conditions. Inelastic compaction was associated with pore collapse that seems to initiate from stress concentrations at the surface of a pore. Cataclasis appeared to develop preferentially around the macropores. Significant mechanical twinning was also observed in samples deformed to relatively high level of strain. To capture these micromechanical processes, we developed a model treating the limestone as a dual porosity medium, with the total porosity partitioned between macroporosity and microporosity. The representative volume element is made up of a large pore which is surrounded by an effective medium containing the microporosity. Cataclastic yielding of this effective medium obeys the Mohr-Coulomb or Drucker-Prager criterion, with failure parameters dependent on porosity and pore size. We applied this model to our new data.