Wellbore decommissioning is the final stage in the life cycle of any oil or gas wells and operates have the obligation to decommission wells safely once they reach to end of their life. Repurposing near-to-decommission wells for storing hydrogen helps in forming a hydrogen-based energy storage system. Hydrogen sourced from surplus renewable electricity (using an electrolyzer) can be compressed into a storage pipe that is secured within the wellbore (within the production casing). This system offers two routes for hydrogen consumption: 1) Power-to-Hydrogen and 2) Power-to-Power. Existing oil and gas tubular designed for mild to medium sour services maybe used to form the storage pipe. The capacity of this storage pipe depends on pipe length and diameter that can fit within the wellbore. This system can potentially integrate green hydrogen into local economies by managing decommissioning costs for the creation of a storage solution for green hydrogen. Figure.1 shows the conceptual design for the proposed hydrogen-based energy storage solution.
The Australian renewable energy contribution to the overall power sector has reached over 30% with the states of Tasmania and South Australia having penetrations of over 88% and 52% respectively on an annual basis (AEMO). The increased penetration of utility renewable generators and rooftop solar panels cause the generation to exceed the demand at many times of the year especially during spring and fall seasons in Australia and mid-day due to diurnal generation from photovoltaics (PVs), and unless there are means to store the excess clean energy, it is usually curtailed due to extremely low electricity prices. The state of South Australia had the highest curtailment of around 513 gigawatts-hour (GWh) followed by the state of Queensland with 339 GWh of curtailed electricity in 2020. These are equivalent to 9,500 and 6,277 tonnes of green hydrogen production potential for South Australia and Queensland, respectively1. Employing Power-to-Hydrogen systems benefit the grid by adsorbing surplus renewable electricity and mitigating grid instability.
This system provides a small-scale storage for green hydrogen generated on site using surplus renewable electricity. The best candidates for repurposing are those wellbores that are geographically located in agricultural areas (local demand for hydrogen exists) and grid connection is also available, so surplus renewable electricity can be utilised for hydrogen production on the site.
The techno-economic analysis for this system indicates that the levelized cost of hydrogen (LCOH) including the storage cost is estimated between 5.22 A$/(kgH2) and 6.50 A$/(kgH2). This cost can potentially reduce with time in line with a decline in the cost of an electrolzser that is identified as the parameter with the highest contribution to cost. The levelized cost of storage (LCOS) is in the range of 1.33─1.66 A$/(kgH2) and further cost reduction is possible if the system is subsided directly by the oil and gas operator/regulator who benefit from wellbore repurposing.
For more information, you may read our article published in International Journal of Hydrogen Energy (https://authors.elsevier.com/a/1fDPQ1HxM4zIWh).