The "critical state" concept of elastoplastic constitutive behavior has been utilized extensively to model the stress-strain response of many geomaterials that undergo plastic yielding. This paper uses a critical state model to investigate the deformation and deformation-induced permeability changes observed in laboratory experiments conducted on siliciclastic and carbonate petroleum-reservoir rocks. We find that the shape of the yield surface has significant impact on post-yield fluid flow response. Differences in behavior between the rock types tested can be explained qualitatively through consideration of differences in the micromechanics of deformation. We find that permeability changes with both stress and strain in general follow a similar constitutive model as deformation. However, we observe experimental behavior not fully accounted for by the critical state concept, due to mechanical complexity on the microstructural level.

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