Scientists from Kyushu University and the ENEOS Xplora research center have proposed an unusual way to produce blue hydrogen directly from oil reservoirs using residual oil, the production of which is usually considered financially unviable. Instead of bringing this feedstock to the surface and processing it at complex facilities, the researchers demonstrated that some of these processes can be transferred underground and combined with the existing enhanced oil recovery technologies.
The proposed concept is based on in-situ combustion supplemented with a new element. Upon the completion of enhanced oil recovery operations, nanoparticles of mineral additives – nickel oxide (NiO) and calcium hydroxide (Ca(OH)₂) – get injected into the reservoir. Oxygen is then fed into the reservoir to ignite some of the remaining oil. The resulting heat is not an end in itself: it serves as a source of high temperature at which the oil gasifies and decomposes to form methane and other light gases, and then it reacts with water vapor to form hydrogen.
During laboratory experiments, the scientists simulated underground reservoir conditions by heating a mixture of sand, oil, water and minerals in a reactor to temperatures ranging from 400 to 800°C. Nickel oxide released oxygen during heating, which enhanced combustion and raised the system’s temperature. Meanwhile, the resulting metallic nickel would act as a catalyst, accelerating the steam reforming of hydrocarbons and methane into hydrogen. Although it increased H₂ yield, this effect was accompanied by enhanced CO₂ formation.
Calcium hydroxide acted differently. It not only facilitated steam reforming but also chemically bound the resulting carbon dioxide, converting it into solid calcium carbonate (CaCO₃), which remained in the rock pores. During experiments with the addition of Ca(OH)₂, the share of hydrogen in the gas mixture reached 42%, some 9% higher than without the mineral additive, while the CO₂ concentration went down. As a result, this mineral simultaneously enhanced hydrogen production and bound carbon with two oxygen atoms directly in the reservoir.
The researchers also demonstrated that up to 70% of the energy potential of the original oil can be converted into useful fuel (hydrogen and methane) at temperatures of about 800°C. At the same time, the use of Ca(OH)₂ significantly reduces the carbon footprint of the resulting gas, which is why this product can be classified as blue hydrogen.
In the future, the scientists propose moving from laboratory testing to experiments on full-size cores. This is needed in order to assess how mineral particles are distributed in real rock and whether they impair formation permeability, as well as how stable the reactions are under formation pressures and real fluid flows. Selecting the minimum required amount of Ca(OH)₂ and NiO also continues to be a challenge, as the cost of nanoparticles remains a key factor limiting the practical application of the proposed technology.
