This paper presents a study of the compaction of petroleum reservoirs applied to very porous carbonate rocks such as chalk. In production estimates made in reservoir engineering, the processing of the mechanical problem is often greatly simplified. Good modelling of how materials behave gives special consideration to the influence of mechanical deformations on fluid recovery. After an analysis of the mechanical behaviour of very porous chalks, an elastoplastic behaviour model is derived so as to reproduce the principal experimental observations. This behaviour model can then be used to perform local simulations of the mechanical behaviour of a reservoir undergoing depletion and thus to demonstrate the importance of the stress path and the initial stress state on the deformation of materials and hence on the recovery rate.