Etude du comportement du grès rouge de Wildmoor. Application à l'analyse de stabilité d'un forage pétrolier en cours de creusement et de production

摘要

This study concerns the mechanical behaviour and the failure conditions of a reservoir rock (red Wildmoor sandstone). Several stress paths, in axisymetric conditions (uniaxial and triaxial compression tests, extension tests), have allowed to characterize the constitutive behaviour of the rock. The material damage is quantified through triaxial compression tests with loading and unloading cycles. The constitutive law developed takes into account the stress and damage dependency of the elastic parameters. The plastic behaviour of the rock is described by a non-linear Mohr-Coulomb criteria which takes into account the pressure dependency of the plastic parameters (friction and dilatancy coefficients). It involves an isotropic friction hardening phase and a kinematic cohesion softening one. This constitutive model is extended to non-coaxial plasticity theory for appropriate prediction of strain localization. Borehole stability during the drilling phase and the production phase is studied. This involves the development of a code to compute the stress field around the borehole during drilling and oil production. The study of the occurence of various instability modes (shear band formation, surface instability) has shown prominentely the influence of the dilatancy of the rock, the depth of the borehole and the pressure gradient applied at the borehole wall during production.