Underground Hydrogen Storage In Porous Media
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The energy transition from fossil fuels to renewable sources is the pathway to attain preventive targets of global warming set by the IPCC. The supply of energy from renewable sources is intermittent and extensively dependent on weather conditions such as the intensity of sunlight and wind velocity. Hydrogen is a promising zero-carbon option that can store surplus produced energy (during windy/sunny periods) at large scale and alleviate the intermittency problem of renewable sources. Further, hydrogen has nearly three times the energy content per mass of gasoline or diesel, and the raw material for its production is abundant water, making it the fuel of the future. Considering hydrogen's advantages, the Indian government has already launched the National Green Hydrogen Mission to generate it from renewable sources. However, because of hydrogen's low density, large storage space is required to store gigawatt hours of energy. Underground hydrogen storage in porous formations (UHSP) such as depleted hydrocarbon reservoirs and saline aquifers offers the much-needed capacity to store large amount of hydrogen. A recent investigation suggests that up to 22610 terawatt hours of energy can be stored as hydrogen in
India's deep saline aquifers. While promising, there are some technical challenges with UHSP: in-situ geochemical and microbial reactions, residual hydrogen trapping, leakage, and water production during hydrogen extraction, which can lower the hydrogen storage efficiency. The injected hydrogen can originate geochemical and microbial reactions leading to a new chemical equilibrium between the rock minerals, dissolved gases, pore water, and the rock matrix. Subsurface reactions in UHSP reservoir may result in the precipitation/dissolution of rock minerals. Further, the bacterial action can lead to the formation of biofilms resulting in pore-clogging. Precipitation/dissolution and pore-clogging can change the porosity and the permeability of the UHSP reservoir, affecting the injection/withdrawal rate of hydrogen. Geochemical and microbial reactions might change the pore fluid properties such as viscosity and density. The change in permeability and pore fluid properties by reactions can trigger interfacial instabilities leading to residual hydrogen trapping, a process by which hydrogen is trapped in the reservoir, making it unrecoverable.
In the proposed work, I will address two challenges that are associated with UHSP. The first one is to quantify the impact of the geochemical and microbial reactions on the UHSP reservoir porosity and permeability. The second is to investigate the effect of geochemical and microbial reactions on interfacial instabilities and residual hydrogen trapping.
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