Evaluating Potential Near Wellbore Integrity Issues in Cement and Casing Layers During Subsurface Hydrogen Storage and Production

Abstract Climate change, and the contribution of greenhouse gases like carbon dioxide and methane towards intensifying this issue have prompted many countries to identify cleaner and greener forms of energy. Hydrogen has risen as a promising alternative stop-gap fuel in this energy transition given that it is cleaner, as well as being an effective energy carrier. Though the use of hydrogen as a fuel is not a new concept, the widespread use of this has been limited by several technological and reliability limitations - including issues in storage and production. Underground storage of hydrogen in depleted oil and gas reservoirs has been considered as a feasible solution, and an alternative to aboveground storage. Significantly large quantities of hydrogen gas can be stored relatively easily, safely and cheaply in such depleted reservoirs, until the hydrogen is needed - when it can be pumped out. However, the innovative idea of storing hydrogen in depleted petroleum reservoirs is also fraught with difficulties and challenges. Several integrity issues need to be considered, especially in the near wellbore region owing to the small size and the relatively high reactivity of the hydrogen molecule. Casing, tubing and the cement layer in the injection/production wells are of particular concern, especially while utilizing existing wells and depleted reservoirs. From the standpoint of subsurface containment, underground hydrogen storage and production is generally feasible, especially by utilizing our knowledge from prior CO2 sequestration initiatives. However, the properties of hydrogen, particularly its small size and reactivity, increase the complexity of underground storage and introduce new challenges and limitations. Casing, Tubulars and other OCTG components are prone to crack and deform when exposed to hydrogen, by a process known as hydrogen embrittlement. Isolation using cement plugs is also challenging since cement is known to degrade in the presence of hydrogen, while the small size of the hydrogen molecule makes containment in older wells difficult. All these need to be evaluated in detail to develop injection and storage criteria, as well as determining the need for cushion gas, and the ultimate recovery when the gas is eventually pumped back to the surface. With increased emphasis on hydrogen as an energy source, it is important to study and identify potential issues associated with its underground containment and storage. Injection/production wells will play a major role in enabling this and properly understanding potential integrity issues with the cement and casing are essential to ensure safe and sustained operations.