Plasticity and strain localization around a horizontal wellbore drilled through a porous rock formation. (March 2016)

• Record Type: Journal Article
• Authors: Spiezia, Nicolò; Salomoni, Valentina A.; Majorana, Carmelo E.
• Is Part Of: International journal of plasticity. Volume 78(2016:Mar.)
• Page Start: 114
• Page End: 144
• Publication Date: 2016-03
• Subjects: B. Elastic-plastic material -- B. Rock -- C. Finite elements -- B. Finite strain -- Wellbore stability; Plasticity -- Periodicals; Plasticité -- Périodiques; Plasticity; Periodicals; 620.11233
• DOI: 10.1016/j.ijplas.2015.10.013
• Languages: English
• ISSNs: 0749-6419

Abstract

Abstract: Predicting plastic deformation and localization band around a wellbore drilled through a porous rock is a challenging task that could have important implications for the prediction of instability and sand production. This study focuses on analyzing stress field, plastic zones, and localized deformations around a horizontal borehole drilled at a great depth through a highly porous rock formation. Several laboratory studies demonstrate that, depending on the loading path, highly porous rocks are susceptible to different failure mechanisms, but most of these mechanisms are mainly due to shear-induced dilation and shear-enhanced compaction. Plasticity models, in conjunction with bifurcation analysis, represent an extremely useful framework for describing such detailed constitutive responses. This paper presents a new elastoplastic constitutive model characterized by two yield surfaces intersecting smoothly, that is able to capture the different failure modes. The model is validated against experimental data for several different porous rocks, and it is then used to determine the stress and strain distributions around a horizontal wellbore using nonlinear finite element analysis. Particular interest is devoted to predicting the condition for the formation of a localized band of intense deformation, elucidating the factors that either prevent or enhance the band initiation. Results of simulations show the key role played by the elastoplastic constitutive model and the effects of the mud pressure, the in-situ stress condition and geometric imperfections in the development and propagation of plastic zone, as well as in the initiation of localization zone. Highlights: An elastoplastic constitutive model has been proposed to describe high porous rocks. The model has been validated against experimental data. The model has been used to predict plasticity and localization around a wellbore. Depending on stress conditions, dilatant and compactant mechanism take place. In situ conditions affect significantly the plasticity and the initiation of bands.