Numerical modelling is used to investigate CO2 injection into geological formations. We begin by using a production simulation model to investigate how faults might impact CO2 movement in the subsurface. We highlight the importance of considering relative permeability and capillary pressure of the fault rocks when modelling CO2-brine flow across the faults. We then investigate the stress path evolution within a reservoir during CO2 injection using a coupled production simulation - geomechanical model