A Mathematical Model for Formation Caprock Integrity Incorporating Creep Deformation Mechanism: A Hydrogen Storage Seasonal Case Study

This research effort aims at addressing the Geo-mechanical aspect of hydrogen underground storage, specifically caprock integrity tests using creep deformation modelling. This study also concentrates on time and injection rate dependent processes which might lead to permanent deformation of reservoir rocks during injection and production cycles due to the cyclical pore-pressure changes. The newly developed model includes a new term that accounts for pore expansion and compaction, and was coupled to the simplified power law. The model was then verified against uniaxial laboratory data and validated by comparing it to the power law model. The idea is to simulate several injection and production cycles of vast amounts of hydrogen into a reservoir that is saturated primarily by saline formation water (aquifer) under certain conditions to assess caprock integrity. In this study, several cycles of hydrogen injection and production seasonal periods are implemented which resulted in cyclical pressure changes on rocks (including stress-strain effect on mechanical behavior of caprocks). During the production period, the pore-pressure decreases and the pore volume decreases drastically resulting in a reduced possibility of rock failure. As for the injection period, the pore-pressure increases and the pore volume increase which resulted in the stress path, moving towards the failure envelope. A cube model was built to examine the effect of the newly developed model on a Japan case study which also showed no critical changes on the pore pressure indicating that the pore expansion and compaction that took place was very minimal.