Póster presentado en la 7th Trondheim Conference on CO2 Capture, Transport and Storage, celebrada en Trondheim (Noruega) del 4 al 6 de junio de 2013. It is usually assumed that CO2 for geological storage should be injected in supercritical (SC) state (i.e. p>7.382 MPa and T>31.04 ºC) to avoid thermal stresses or phase changes in the injection tubing or in the formation. Injecting CO2 in liquid phase would be desirable because its density is much larger than that of either gaseous or supercritical CO2. Since most of the wellhead pressure is required for overcoming buoyancy forces in the wellbore, increasing density in the wellbore translates into a parallel reduction of the required wellhead pressure. Yet, most projects contemplate injection in either SC or gaseous phase because of concerns about (1) phase changes in the wellbore, or (2) thermal stresses in the reservoir caused by the injection of CO2 much colder than the reservoir. We perform numerical simulations to analyze the thermodynamic evolution of CO2 and the thermo-hydro-mechanical response of the formation and the caprock to liquid CO2 injection. We find that injecting CO2 in liquid state is energetically more efficient than in SC state because liquid CO2 is denser than SC CO2, leading to a lower overpressure not only at the wellhead, but also in the reservoir because a smaller fluid volume is displaced. Cold CO2 injection cools down the formation around the injection well. Further away, CO2 equilibrates thermally with the medium in an abrupt front. A slight temperature increase occurs in the SC CO2 region that is due to the exothermal dissolution of CO2 into the brine. The liquid CO2 region close to the injection well advances far behind the SC CO2 interface. While the SC CO2 region is dominated by gravity override, the liquid CO2 region displays a steeper front because viscous forces dominate (liquid CO2 is not only denser, but also more viscous than SC CO2). The temperature decrease close to the injection well induces a stress reduction due to thermal contraction of the media. This can lead to shear slip of pre-existing fractures in the aquifer for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mobilized friction angle in the seals is not increased when injecting liquid CO2 and it is even reduced in stress regimes where the maximum principal stress is the vertical. We conclude that injecting CO2 in liquid state rather than SC is favourable for several reasons: (1) this injection strategy is energetically advantageous, (2) no transformation operation or only low energy consumption conditioning operations are necessary, (3) a smaller compression work at the wellhead is necessary because of the smaller compressibility of liquid CO2, (4) since liquid CO2 is denser than SC CO2, liquid CO2 injection induces a lower overpressure also at within the aquifer because a smaller amount of fluid is displaced and (5) the caprock mechanical stability is improved. Peer reviewed