## 1 Introduction  
The residual and solubility trapping of CO\({}_{2}\) in the saline aquifer maximize the storage capacity and ensure the reservoir integrity of CO\({}_{2}\) sequestration [1]. After CO\({}_{2}\) is injected into target reservoirs, it migrates in permeable rock under a supercritical state and dissolves into brine to form carbonic acid [2]. The dissolution process reduces the risk of CO\({}_{2}\) leakage through the caprock of the reservoir due to the upward movement of the CO\({}_{2}\) plume under the buoyancy effect [3]. The dissolution rate of CO\({}_{2}\)-brine, which represents the mass transfer process, serves as an important parameter to immobilize the free-phase CO\({}_{2}\). The major driving force of the dissolution rate is the partitioning non-equilibrium concentration and is controlled by the interfacial and environmental conditions in the porous media [4]. If the pore space is occupied by the brine with high CO\({}_{2}\) concentrations, the dissolution rates will be reduced, increasing the time spans of the CO\({}_{2}\) precipitation from hundreds to thousands of years. Depending on the stage of CO\({}_{2}\) sequestration and the physical properties of the saline aquifers, diffusion, advection, and convection can occur during the mass transport [5]. Through these mechanisms, the CO\({}_{2}\) near the two-phase interface is dissolved and transported away. Then, further fresh brine imbibes into the in situ pores and sequentially makes contact with free-phase CO\({}_{2}\), accelerating the dissolution process. To determine the dissolution rate of the injected CO\({}_{2}\), scaling analysis based on simulation and experiments of the convective mixing and non-equilibrium imbibition have been applied to characterize the effect of convection and diffusion [6; 7; 8]. In previous studies, the dissolution process was widely investigated between the non-wetting phase (air/non-aqueous phase liquid) and the nearby wetting phase (water/brine) in porous media. For the observation focused on a single pore or a cluster and connected pore throats, the dissolution is dominated by molecular diffusion and mass transfer at the CO\({}_{2}\)-water interfacial area [9]. Besides, in a 2-D model, the observed convection and dissolution rates are mainly an effect of dispersion due to the transport velocity of the solvent phase. Dynamic measurement of the dissolution process is necessary to determine the potential impacts of the above mechanisms on the dissolution rate. During the CO\({}_{2}\) dissolution, brine saturated with CO\({}_{2}\) will be removed more effectively from the CO\({}_{2}\)-brine interface and more unsaturated brine comes into contact with the CO\({}_{2}\). This process will be affected by the actual formation environment, including the reservoir temperature and pressure, flow development, heterogeneity, pore structure, and gas distribution [10]. In addition, the flow rate of the brine in the aquifer could be regarded as constant, while in the background, the flow CO\({}_{2}\) plume pushes the in situ brine to move forward at different flow rates. Thus, different CO\({}_{2}\) injection rates will result in the various dissolution rates of CO\({}_{2}\) at the field scale. Despite its recognized importance, measurement of the accurate dissolution rate of CO\({}_{2}\) into brine in realistic subsurface conditions is challenging due to the difficulty of conducting large-scale numerical simulations and experiments with reservoir complexity [11; 12; 13]. As the depth of target reservoir increases, CO\({}_{2}\) turns into the supercritical state because temperature and pressure surpass the critical point of the gas. In this state, compared to gaseous CO\({}_{2}\), supercritical CO\({}_{2}\) exhibits unique characteristics such as a high density, low viscosity, and high diffusivity and solubility. However, the studies of the effect of CO\({}_{2}\) phase state on dissolution rate are insufficient.