Mechanical behaviour of a porous chalk and effect of saturating fluid

This paper presents an experimental investigation and numerical modelling of the behaviour of a porous chalk by taking into account effects of saturating fluid. Two representative fluids, oil and water are considered. The laboratory testing programme includes two topics. First, conventional hydrostatic and triaxial compression tests are carried out on samples which are saturated with water and oil, respectively. The sensitivity of chalk behaviour to saturating fluid is clearly shown. Secondly, specific water injection tests are conducted in which water is injected into chalk samples initially saturated by oil, under different hydrostatic and deviatoric stress states. Additional plastic deformation induced by water flooding is determined. In the second part of paper, an elastoplastic model with two yield surfaces is proposed. The water-induced plastic deformation is described by introducing an additional plastic mechanism related to the behaviour jump between two material states of chalk. An overall good correlation is obtained between numerical simulations and experimental data not only for conventional tests, but also for water injection tests. Copyright © 2000 John Wiley & Sons, Ltd.