Non-Destructive Cyclic Analysis of Sealing Ability of Well Cement for Seasonal Underground Hydrogen Storage.

Underground hydrogen storage (UHS) is one potential solution that could provide a steady source of clean energy to the globe. Given their infrastructure, depleted hydrocarbon reservoirs may be a suitable storage option. However, ensuring wellbore integrity is a significant challenge when storing hydrogen in such reservoirs. In this study, 3.81 × 7.62 cm cement samples were cured for 12 and 18 months and were cyclically exposed to hydrogen for three 28-day cycles at 10.34 MPa and 50 °C. The pressure increment was achieved at the rate of 2.06 MPa/hr. The cement's porosity, permeability, and ultrasonic velocity were tested before and after each cycle. To investigate the changes in the surface structure and elemental composition, scanning electron microscopy (SEM) was conducted. The results illustrate increased porosity and permeability, but the ultrasonic velocity changes were insignificant. The SEM images do not exhibit any change in the microstructure. However, energy dispersive spectroscopy (EDS) mapping exhibited mineral dissolution. This study demonstrates how cyclic exposure to hydrogen will affect the integrity and the sealing ability of aged cement, which will be an essential factor to consider while repurposing existing oil and gas wells to hydrogen injectors or producers for UHS applications in depleted hydrocarbon reservoirs. [ABSTRACT FROM AUTHOR]