Underground hydrogen storage: Integrated surface facilities and fluid flow modelling for depleted gas reservoirs

We report a new techno-economic model to assess performance and capital costs for large-scale underground hydrogen storage in depleted gas reservoirs. A simulation toolbox is developed to model surface facilities and to simulate the hydrogen flow in geological formations in an integrated fashion. Integrated modelling revealed the following key insights: 1) A buffer system is highly desirable to absorb inherent variability in upstream hydrogen production; 2) hydrogen mixing with existing gases in the reservoir, together with gravity segregation and diffusion, results in a decline in hydrogen purity at the wellhead over time and can require increased purification; 3) the capital cost is dominated by the cost of cushion gas (hydrogen) and the compression system where about 9% of the total energy content of the hydrogen is consumed for compression. The scenarios modelled in our study result in a levelized cost of storage in Australia ranging from 2.3 to 4.29 A$/(kg).