## 3 Reservoir-Scale Simulations
### Coupled Flow-Geomechanical-Geochemical Processes  
It has been observed that several studies have separately addressed geomechanical or geochemical effects, but, due to the nature of the geological carbon storage sites, rocks are exposed to both mechanical loading and geochemical alterations caused by the injection of CO\({}_{2}\). The impact on the plume flow of poromechanical loading also depends on whether the media is simultaneously experiencing chemical alterations. Therefore, evaluating the connection, and potential coupling, between geo-chemical and -mechanical alterations needs to be considered. Compared to a solely geochemical and geo-mechanical investigation, which does not provide a thorough analysis of caprock integrity, few studies have addressed coupled chemical-mechanical processes caused by CO\({}_{2}\) injection [93]. The interaction of CO\({}_{2}\) and brine on rocks can alter the frictional properties of faults, thus creating a seismicity hazard [112]. Furthermore, these studies focused on reservoir storage and ignored the seal integrity. For example, [PERSON] et al. [122] performed two-way coupling modelling to simulate the CO\({}_{2}\) plume movement with geochemical reactions and geomechanical effects within the reservoir. The authors of the study concluded that vertical displacement was observed during the injection, and also noted porosity and permeability changes near the wellbore. In contrast, only a limited number of experimental studies [112; 123; 124] have examined the coupled chemical-mechanical behaviour of the seal resulting from CO\({}_{2}\) intrusion. Most of these studies have focussed on using carbonate-rich caprock samples, along with enormous CO\({}_{2}\) partial pressure, to observe obvious chemical alterations within limited experimental times. However, [PERSON] et al. [124] found that it was the spatial distribution, rather than the abundance, of the least-reactive mineral that governed the evolution of the transmissivity of the caprock. Hence, the spatial heterogeneity in minerals can result in barriers to flow, as well as wormholing. They further found that the non-reactive areas present in heterogeneous fractures were not chemically-eroded and could therefore continue to provide mechanical support, which weakens the coupling between geochemical and geomechanical effects. [PERSON] et al. [83] also demonstrated the role of heterogeneity and the effects of coupled chemical-mechanical processes on the reservoir and caprock during carbon storage sequestration. Their key findings included the observation that, for Morrow shale, mineral precipitation resulted in a \(\sim\)25% decrease in porosity at the caprock-reservoir boundary, reducing the potential for CO\({}_{2}\) ingress, and, furthermore, that the caprock seal efficiency was not affected in terms of its mechanical stability, due to the low risk of induced fractures. This is in contrast with other studies, where chemical changes were found to have a great mechanical effect, for example, changing fault behaviour, which was neglected in this work. In other works, [PERSON] [125], and [PERSON] et al. [126] investigated the impact of coupled chemical-mechanical processes on the caprock sealing performance and their results showed that after thousands of years of exposure, only the lowest few meters of the caprock may be affected by the CO\({}_{2}\)-rich fluid, and the effect on its mechanical properties were minor. Although a few studies have been performed including both fully coupled chemical-mechanical effects, together with two-phase flow modelling of CO\({}_{2}\) injection into a relatively uniform geological formation, only minor attention has been given to the impact of impermeable inter-layers on directing plume migration during and after CO\({}_{2}\) injection into a geological formation.