## 1 Introduction  
One of the major causes of global warming is the excessive emission and accumulation of greenhouse gases in the atmosphere, especially carbon dioxide (\(\mathrm{C}\mathrm{O}_{2}\)). One of the methods to control the increase in global temperature is \(\mathrm{C}\mathrm{O}_{2}\) storage in subsurface geological formations. This method has been in practice since the early 1970s [1]. Knowledge concerning mature technologies has been gained from the injection and storage of \(\mathrm{C}\mathrm{O}_{2}\) from many existing enhanced oil recovery and acid gas projects [2, 3]. In addition, several commercial sequestration projects are functioning nowadays, such as the Sleipner, Weyburn, and In Salah projects, and these indicate that it is feasible to store \(\mathrm{C}\mathrm{O}_{2}\) in geological formations as a promising solution for reducing \(\mathrm{C}\mathrm{O}_{2}\) emissions to the atmosphere [4]. The geological formation should have certain characteristics, including that the depth should be greater than 800 m below the ground surface, with acceptable porosity and permeability to store a significant amount of \(\mathrm{C}\mathrm{O}_{2}\). Additionally, for the \(\mathrm{C}\mathrm{O}_{2}\) to be stored safely for thousands of years, it is necessary for the storage formation to have an overlying impermeable confining layer, commonly referred to as caprock or seal. The main geological storage units that have the aforementioned features are depleted oil and gas reservoirs and, in addition, deep saline formations [5]. \(\mathrm{C}\mathrm{O}_{2}\) sequestration is not a straightforward process, since challenges may arise during \(\mathrm{C}\mathrm{O}_{2}\) storage such as maintaining the integrity of an impermeable caprock layer. Caprocks generally fall into three main types: (i) argillaceous rocks, which are highly compacted clays,shales, or mudstones; (ii) consolidated clastic rocks, which have been compacted and highly cemented due to long-term diagenesis; and (iii) evaporites, which are precipitated chlorides, sulphates, and carbonates [6]. The caprock provides a seal against the upwards leakage of free CO2 or CO2-saturated reservoir brine, caused by the buoyancy force, into the overlying strata and back to the atmosphere. The rise of buoyant supercritical (sc)-CO2 plumes is expected to continue for centuries, if not thousands of years, until the CO2 eventually dissolves into the formation brine. The generally accepted target for the allowable leakage rate is that it should be limited to <1% [6]. As shown schematically in Figure 1, in this review we first survey previous experimental work considering the geochemical interactions of CO2 with caprocks and inter-layers, and the resulting evolution of the mineralogy, pore structure, and transport properties, with special attention paid to work on the caprock of the Sleipner field, namely, the Nordland shale. This survey also highlights areas where conflictual findings have been obtained concerning the apparent changes to rocks following exposure to scCO2 due to the limitations of the structural characterisation methods used. We then go on to describe novel or rarely-used rock core characterisation techniques that have recently been shown to resolve some of the conflictual findings that have emerged from the said experimental geochemical studies, but which are not generally discussed in the literature in this area. Finally, in this review we consider field-scale, reservoir simulations of scCO2 sequestration that include flow, geochemical, and geomechanical phenomena in various combinations, with a view to demonstrating the need to include all three in order to obtain truly physically representative field-scale simulations that can include all effects, including counter-intuitive ones, that would be unanticipated without the comprehensive simulation of the sequestration processes. The importance of considering all three coupled processes is rarely examined.