## 1 Introduction  
An essential component of the energy transition to a low-carbon, more sustainable future is hydrogen. It is the perfect fuel for a low-carbon energy system because it is a clean energy source [1]. The decarbonization of the energy system can be aided by producing hydrogen using renewable energy sources like solar and wind power. By doing so, it can be ensured that electricity is available when needed and assists in balancing the system [2, 3]. These considerations underscore the need for comprehensive research, such as the study presented here, to address the challenges and potential benefits of storing hydrogen in depleted hydrocarbon reservoirs. Because hydrogen has the potential to lower CO2 emissions and support a low-carbon energy sector, research on hydrogen as a clean energy source has attracted a lot of attention [4]. Hydrogen is produced via various techniques, including electrolysis and methane fusion, underscoring the significance of large-scale, secure storage. Maximum hydrogen recovery is made possible by naturally occurring sealing qualities in underground storage solutions like salt and rock caverns. However, they have a limited capacity and are only available in certain areas. Although saline aquifers guarantee excellent hydrogen purity and have a huge storage capacity, they also produce a lot of water and have inadequate geological classification. On the other hand, depleted reservoirs have the advantage of already existing infrastructure and well-characterized formations, but they also carry the possibility of leakage, which might be expensive to maintain the infrastructure [5]. Depleted hydrocarbon resources are the most appropriate because hydrogen can be produced and delivered similarly to natural gas, and existing gas infrastructure can be converted to hydrogen use. Hydrogen storage in abandoned oil and gas reservoirs is an affordable solution. However, it is important to note that this approach also has certain disadvantages, including the possibility that residual gas or oil would lower the purity of the hydrogen, and the hydrogen may harm the reservoir's top seal [6]. The different challenges associated with underground hydrogen storage in depleted hydrocarbon reservoirs are presented in Figure 1. However, difficulties with wellbore integrity could be the leading cause of problems during the injection and withdrawal of hydrogen [7]. The well integrity issues are primarily related to the steel casing and the annular cement. Hydrogen embrittlement (HE) is frequently observed in high-strength steels with tensile strengths exceeding 1000 MPa. It is triggered by the accumulation of hydrogen atoms in trapping sites, especially near grain boundaries. This type of damage can be reversed and usually requires an outside stressor. In contrast, low-strength steels with a tensile strength below 1000 MPa are particularly susceptible to hydrogen-induced cracking (HIC), which is brought on by internal pressure from the production of hydrogen molecules. HIC does not require external stress and causes irreparable damage. Hydrogen blistering (HB) primarily affects low-strength steels or materials with soft zones, also below 1000 MPa, and happens when hydrogen molecules gather in trapping sites near the surface [7]. Previous studies have indicated that the impact of CO\({}_{2}\) on cement seals is relatively minimal, suggesting limited degradation and a minor effect on the integrity of wellbores [8; 9]. However, recent investigations have shed light on the role of geochemical processes between cement and CO\({}_{2}\), revealing that these interactions can enhance porosity within the cement structure, consequently leading to degradation [10; 11; 12]. This degradation occurs as CO\({}_{2}\) dissolves into the surrounding formation brine, resulting in the formation of carbonic acid, which in turn initiates the breakdown of the cement [13; 14; 15].