Numerical Modelling of Hydrogen Diffusion in Elastomeric Materials to Evaluate Wellbore Integrity for Hydrogen Injected Well
Authors: Alhassan Yousef , Hossain Md Mofazzal 
Published: February 2024

Abstract
Hydrogen as an energy source is considered one of the most viable alternative solutions to meet ever-increasing energy demand yet minimize the environmental damage and combat the climate change challenges. The massive scale of hydrogen production is essential to replace the reliance on fossil-based energy sources, which pose enormous challenges in storing hydrogen. The concept of Underground Hydrogen Storage (UHS) in depleted hydrocarbon reservoirs attracts significant attention from scientists, engineers, and technocrats worldwide as one of the most promising solutions to hydrogen storage issues. The UHS process involved drilling and injection of hydrogen underground into the reservoirs. The injected hydrogen can potentially change the reservoir's physical characteristics and interact chemically with the formations, nearby wellbore, casing, cement and completion equipment, and other associated components. This study focuses on assessing the impact of hydrogen diffusion through the completion hardware, especially elastomeric packers on the well integrity from both short and long-term perspectives.
Packers utilized for the oil and gas industry to isolate annulus during oil and gas injection/production are usually employed in UHS wells for cost reduction after oil and gas reservoirs are depleted. Most of the packers are manufactured from elastomers designed for oil and gas wells. The physical and thermodynamic properties of oil and gas substantially differ from those of Hydrogen, posing tremendous concerns regarding the containment of Hydrogen and sustainability of UHS applications. This study aims to evaluate the potential of hydrogen escape and loss as well as the integrity of elastomeric materials for subsurface applications using the Computational Fluid Dynamic (CFD) based widely acceptable commercial simulator, ANSYS-Fluent. Three different types of elastomeric materials are examined: Fluoroelastomer (FKM), Hydrogenated Nitrile Butadiene Rubber (HNBR), and Nitrile Butadiene Rubber (NBR). Based on numerical simulation and sensitivity study, FKM has appeared to be a better choice for underground hydrogen storage applications, whereas HNBR and NBR come in second and third best choices, respectively. This is because there seems to be a minimum hydrogen mass fraction travelled radially into the material. Strong impedance to hydrogen diffusion demonstrates FKM's capability to be an annulus-confined material due to its internal properties to prevent diffusion. Overall, despite the variation in hydrogen loss, the research demonstrated that there is an inconsiderable amount of hydrogen diffusion, warranting insignificant implications to subsurface application in normal cases. However, it is highly recommended to perform experimental work to further verify this conclusion as material mechanical properties are observed to degrade when hydrogen is encountered, especially at higher temperatures and pressure. As part of the research objectives, a sensitivity study is conducted to evaluate the most sensitive parameter in hydrogen diffusion phenomena. Temperature appears to be explicitly the most sensitive parameter which can highly influence the density, viscosity, and other properties of the diffused hydrogen. An increase in temperature is observed to considerably increase the diffusion rate through the material, meaning such a level of diffusion can pose a potentially detrimental effect, especially in the long-term integrity of the well.