Reservoir rocks can undergo irreversible deformation (dilatancy or compaction) as a result of a change in effective stress during production of hydrocarbon or during CO2 storage. In this study, we investigated the mechanical behavior of the Chauvigny limestone. It is one of the rocks, which constitutes the Dogger, a deep saline aquifer, one of the favorable geological reservoirs for CO2 storage in France. To investigate the brittle-ductile transition in this limestone, we performed triaxial experiments, at confining pressure in the range of 5-100 MPa. In addition, the evolutions of elastic wave velocities were measured periodically with loading. Our results show that diltatant (nucleation and propagation of cracks) and compaction micro-mechanisms (plastic pore collapse) compete. Two limit cases can be distinguished. During hydrostatic compression, the inelastic volumetric strain seems to be mainly associated with plastic pore collapse, whereas for the triaxial experiments at confining pressure < 30 MPa, the inelastic volumetric strain seems to be mainly associated with the development of shear-induced cracks. For the triaxial experiments at confining pressure > 30 MPa, we are able to distinguish a first critical stress state where plastic pore collapse occurs, and a second stress state where shear-induced cracks are initiated.