A transition towards a low-carbon economy requires carbon geological storage. Carbon dioxide has been injected in the subsurface for several decades for enhanced oil recovery. However, carbon geoleogical storage requires more stringent controls on assuring reservoir integrity during injection, predicting seal capacity over long times and achieving high pore volume occupancy (the opposite of a recovery ratio). This talk discusses selected examples that highlight the importance of chemo-thermo-hydro-mechanical coupled processes for economic and reliable CO2 geoleogical storage. These examples include: potential fracturing at the injector, fault reactivation, structural seal capacity, and undrained poroelastic reservoir monitoring.