The impact of constitutive modeling of porous rocks on 2-D wellbore stability analysis Lu ´ cia Carvalho Coelho a, * , Antonio Claudio Soares b,1 , Nelson Francisco F. Ebecken c,2 , Jose ´ Luis Drummond Alves a,3 , Luiz Landau a,4 a COPPE/Federal University of Rio de Janeiro, Caixa Postal 68552, Rio de Janeiro, RJ CEP 21949-900, Brazil b Petrobras Research Center, Cidade Universita ´ria, Quadra 7, Ilha do Funda ˜o, Rio de Janeiro, RJ CEP 23458-000, Brazil c COPPE/Federal University of Rio de Janeiro, Caixa Postal 68506, Rio de Janeiro, RJ CEP 21949-970, Brasil Received 23 September 2003; accepted 25 August 2004 Abstract It is well established that a wellbore may fail under tension or shear compressive modes. Recently, the behavior of porous rocks has been studied, showing that they may fail because of hydrostatic compression. Cap models may represent the compacting behavior of porous rocks. This work presents a comparison among Drucker–Prager, Mohr–Coulomb, and cap model in wellbore stability analysis for a borehole drilled in 30% porosity limestone from a deep water reservoir, Campos Basin, offshore Brazil. It shows that traditional models used in wellbore stability analysis may lead to erroneous conclusions about the stability in the vicinities of the borehole. D 2004 Elsevier B.V. All rights reserved. Keywords: Wellbore stability; Compaction bands; Pore collapse; Constitutive models 1. Introduction Efforts introduced in the rock caused by drilling and production may reach the strength of the material, leading to its failure. The theory of elastic plasticity has been extensively used to evaluate the stability of wellbore. It is well established that hydrocarbon wellbores fail under tension mode or shear compressive mode (Fjaer et al., 1992; McLean and Addis, 1990; Morales et al., 2000). Many constitutive models were proposed to evaluate well- 0920-4105/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2004.08.004 * Corresponding author. Tel.: +55 21 2562 8419; fax: +55 21 2562 8414. E-mail addresses: lucia@lamce.ufrj.br (L.C. Coelho)8 aclaudio@cenpes.petrobras.com.br (A.C. Soares)8 nelson@ntt.ufrj.br (N.F.F. Ebecken)8 jalves@lamce.ufrj.br (J.L.D. Alves)8 landau@lamce.ufrj.br (L. Landau). 1 Tel.: +55 21 3865 6896; fax: +55 21 3865 6795. 2 Tel.: +55 21 2562 7388; fax: +55 21 2562 7392. 3 Tel.: +55 21 2562 8416; fax: +55 21 2562 8414. 4 Tel.: +55 21 2562 8415; fax: +55 21 2562 8415. Journal of Petroleum Science and Engineering 46 (2005) 81 – 100 www.elsevier.com/locate/petrol