Summary In many wellbore stability analyses, the ability to forecast both the occurrence and extent of plastic deformation and failure hinges upon a fundamental understanding of deformation mode and failure mechanism in the reservoir rock. This study focuses on analyzing plastic zones, localized deformations, and failures around a borehole drilled overbalanced or underbalanced through a highly porous rock formation. Based on several laboratory experiments, porous rocks are prone to deform under both shear‐induced dilation and shear‐enhanced compaction mechanisms depending on the stress state. The shapes of the deformation and failure patterns around the borehole are shown, depending on the initial stress state and the local stress paths. The inquiry of the local stress paths in the near‐wellbore zone facilitates the understanding of the reasons for different types of failure mechanisms, including the mixed‐mode and the plastic deformation structures. The modification of the 2D plane strain condition by imitating third stress in the numerical scheme helps us bring the stress paths closer to the real state of loading conditions. Our modeling reveals that the transition from isotropic to anisotropic stress state is accompanied by an increase in the deviatoric part of effective shear tensor that leads to the development of inelastic deformation, degradation, and subsequent rock failure. Particular interest is devoted to the modeling of strain localization especially in compaction mode around a wellbore and computing the amount of stress concentration at the tips of dog‐eared breakouts. Stress concentration can result in a change in irreversible deformation mode from dilatancy to compaction, elucidating the formation of the shear‐enhanced compaction phenomenon at the failure tips in the direction of the minimum horizontal stress.

revue des re ´alisations fondamentales de la tectonophysique russe dans le domaine des e ´tudes des contraintes naturelles et de la mode ´lisation des structures des de ´formations est ici pre ´sente ´e. Il est aussi discute ´de questions relatives a `la physique des tremblements de terre et aux me ´canismes ge ´ne ´rateurs de contraintes de ´viatoriques dans l'e ´corce terrestre.ß 2012 Acade ´mie des sciences. Publie ´par Elsevier Masson SAS. Tous droits re ´serve ´s.

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In this study various approaches are used to estimate components of the stress fields and the directions of the principal axes of the stress tensor in a geological object complicated by disjunctive disturbances. Two approaches are used: one is the cataclastic analysis method and the other one is finite element method. The initial data for modeling are the results of the interpretation of the seismic cube and the mechanical properties of the layers of the studied object.

Ce nume ´ro spe ´cial du CR Geoscience re ´sulte d'une initiative de Jacques Angelier, soutenue par Fedor Yakovlev, qui avaient propose ´de co-e ´diter les actes d'une confe ´rence rassemblant diffe ´rents instituts de recherche de la fe ´de ´ration des e ´tats de Russie, tenue a `Moscou du 13 au 17 octobre 2008 sur le the `me de la Tectonophysique et d'autres proble `mes d'actualite ´pour les Sciences de la Terre. Cette confe ´rence ce ´le ´brait aussi le 40 e anniversaire du laboratoire de Tectonophysique fonde ´a `l'Institut de physique de la Terre de l'Acade ´mie russe des sciences par le professeur Gzovsky.Cette confe ´rence comprenait 134 pre ´sentations orales et 60 posters pre ´sente ´s par des chercheurs provenant de 26 villes de Russie et de 13 autres re ´publiques de la confe ´de ´ration, i.e. l'Ukraine, l'Ouzbe ´kistan, le Kyrgyzstan, le Kazakhstan et la Ge ´orgie. Les principaux the `mes aborde ´s e ´taient les suivants :Contents lists available at SciVerse ScienceDirect