Implications of Underground Hydrogen Storage on the Sealing Ability of Aged Cement
Authors: Hussain A. , Emadi H. , Thiyagarajan S. R. , Maury Fernandez D. , Ispas I. , Watson M. 
Published: August 2024

ABSTRACT:
Encouraging the utilization of renewable energy is critical for addressing our energy demands, but large-scale storage is required for it to be feasible. 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 18 months and were cyclically exposed to hydrogen for three 28-day cycles at a maximum pressure of 10.34 MPa and 60°C. The pressure increment was achieved at the rate of 2.06 MPa/hour. The cement's porosity, permeability, and ultrasonic velocity were tested before and after each cycle. Following the ultrasonic velocity measurements, the dynamic elastic properties were calculated. To investigate the changes in the structure and elemental composition before and after exposure on the surface, 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, 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.

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(Canbaz et al., 2021). The decarbonization of the energy system can be aided by producing hydrogen using renewable energy sources like solar and wind power (Bechara et al., 2022; Bechara, Gamadi, Thiyagarajan, et al., 2023; Bechara, Gamadi, Watson, et al., 2023). Since hydrogen has a long storage life, it is an essential energy storage component for sporadic renewable energy sources like wind and solar energy. By doing so, you can ensure that electricity is available when needed and assist in balancing the system (Canbaz et al., 2021). Aquifers, depleted hydrocarbon reservoirs, and salt caverns are all capable of storing significant amounts of hydrogen for a long time. 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(Al-Hadrami et al., 2022).
Hydrogen storage in abandoned oil and gas reservoirs is an affordable solution. Nevertheless, there are certain disadvantages to this approach as well, including the possibility that residual gas or oil would lower the purity of the hydrogen, impurities in the reservoir may have an impact on purity (Thiyagarajan et al., 2022).