## 1 Introduction
This analysis will be addressed during this comparison, as well as the better equilibrium between gravity and viscous forces provided by horizontal wells due to the main contribution of vertical permeability for the flow, reducing the buoyancy CO\({}_{2}\) flux. The idea that the mass of residually trapped CO\({}_{2}\) is enhanced, when the plume migrates in the lateral direction was observed numerically by [PERSON] et al. [16], who investigated different levels of vertical and horizontal permeabilities in a model with a source point of injection. In the conclusion section of this work, the authors postulated that horizontal wells can be a likely means to increase the lateral extension of CO\({}_{2}\) plumes, taking advantage of the residual trapping mechanism. However, they did not simulate cases with horizontal wells, as is in the goals of our current study. In addition to that, our paper aims to expand the study by [PERSON] et al. [17]. They compared vertical and horizontal wells to store CO\({}_{2}\) in saline aquifers but did not consider the effect of hysteresis as a trapping mechanism, because their investigation was focused only on the injection time (50 years), where the system only underwent the drainage path. In other words, our work intends to evaluate the long-term CO\({}_{2}\) storage, modeling all of the trapping mechanisms that can occur. Therefore, the innovative aspects of our work are summarized below:  
* Providing technical arguments in favor of using horizontal wells in low- and mid-permeability targets (average less than 100-200 mD), considering the greater mass of CO\({}_{2}\) trapped as a residual fluid and the better equilibrium between gravity and viscous forces to control the CO\({}_{2}\) buoyancy, evaluating long-term storage (thousands of years of redistribution);
* Proposing a practical way to design the horizontal well length to maximize the CO\({}_{2}\) entrapment and make the flow less gravity-driven;
* Evaluating the impact of both strategies (vertical and horizontal injectors) on the risk of CO\({}_{2}\) penetration into the caprock, considering adsorption, diffusion, and the Darcy reactive flow. The horizontal wells are applied in actual operating CCS projects worldwide. Sleipner in the North Sea and In Salah in the Sahara Desert are examples of storage sites with horizontal injectors [18]. Therefore, the broader impact of this research is intrinsically related to better control of the CO2 plume redistribution, which has the following advantages:  
1. Preventing an unexpected and undesired interaction with the caprock, mainly related to the risk of CO2 leakage due to fault/fracture activation or the creation of new fractures when the injection exceeds the minimum rock strength [19; 20]. In addition, related to the geochemical reactions among the CO2\(-\)prime\(-\)mineral system, which can affect the integrity of caprock and its sealing capacity with alteration in its petrophysical properties induced by mineral changes [21];
2. Better control and monitoring of the CO2 plume propagation to the CCS project evaluation with data from the injection or observation/monitoring wells, besides geophysical data, such as time-lapse seismic, vertical-seismic profiles (VSPs), and micro-seismic [5];
3. Providing insights into the CO2 storage in depleted oil/gas reservoirs where it is possible to use existing horizontal and multilateral wells. The following conditions are outside the scope of this paper:  
* Consideration of impurities and free water content in CO2 stream injected;
* Modeling the dry-out effect due to water vaporization with CO2 injection or another injectivity issue, which can be found in [PERSON] et al. [22];
* CO2 leakage through wells with poor cement jobs, as pointed out by [PERSON] et al.