INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS Int. J. Numer. Anal. Meth. Geomech., 2006; 30:1477–1500 Published online 9 August 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/nag.543 Modelling mechanical behaviour of limestone under reservoir conditions Lu´cia Carvalho Coelho 1, * ,y , Antonio Claudio Soares 2,z , Nelson Francisco F. Ebecken 3,} , Jose´ Luis Drummond Alves 1,} and Luiz Landau 1,k 1 COPPE/Federal University of Rio de Janeiro, Caixa Postal 68552 CEP 21949-900, Rio de Janeiro-RJ, Brazil 2 CENPES - Petrobras Research Centre, Cidade Universita ´ria, Quadra 7, Ilha do Funda ˜o, CEP 23458-000 - Rio de Janeiro, RJ, Brazil 3 COPPE - Federal University of Rio de Janeiro, Caixa Postal: 68506 CEP 21945-970, Rio de Janeiro-RJ, Brazil SUMMARY High porosity and low permeability limestone has presented pore collapse. As fluid is withdrawn from these reservoirs, the effective stresses acting on the rock increase. If the strength of the rock is overcome, pore collapse may occur, leading to irreversible compaction of porous media with permeability and porosity reduction. It impacts on fluid withdrawal. Most of reservoirs have been discovered in weak formations, which are susceptible to this phenomenon. This work presents a study on the mechanical behaviour of a porous limestone from a reservoir located in Campos Basin, offshore Brazil. An experimental program was undergone in order to define its elastic plastic behaviour. The tests reproduced the loading path conditions expected in a reservoir under production. Parameters of the cap model were fitted to these tests and numerical simulations were run. The numerical simulations presented a good agreement with the experimental tests. Copyright # 2006 John Wiley & Sons, Ltd. Received 13 April 2005; Revised 12 June 2006; Accepted 14 June 2006 KEY WORDS: pore collapse; plasticity; stress paths; cap models; reservoir geomechanics *Correspondence to: L. C. Coelho, COPPE/Federal University of Rio de Janeiro, Caixa Postal 68552 CEP 21949-900, Rio de Janeiro-RJ, Brazil. y E-mail: lucia@lamce.ufrj.br z E-mail: aclaudio@petrobras.com.br } E-mail: nelson@ntt.ufrj.br } E-mail: jalves@lamce.ufrj.br k E-mail: landau@lamce.ufrj.br Copyright # 2006 John Wiley & Sons, Ltd.