Biogenic hydrogen production from residual oil in geological carbon storage sites

We found that the combined supply of protein-rich matter and supercritical CO₂ to petroleum produced water (PW) stimulates the biogenic production of H₂ from dissolved oil hydrocarbons by indigenous microbial communities of oil reservoirs. Our experimental results support the hypothesis that a decrease in pH to acidic levels due to the dissolution of supercritical CO₂ into the aqueous phase and the availability of protein-rich matter, favors the activity of H₂-producing microbial communities over the activity of H₂-using microbial communities. To determine where, when, and how much H₂ could be produced in a depleted oil reservoir co-injected with CO₂ and PW supplied with protein-rich matter, we simulated the biogenic production of H₂ for the Morrow B sandstone reservoir. Our simulation results indicate that 365 – 1925 kg of H₂ could be produced after 100 days of CO₂ and PW co-injection (1.5 kg-CO₂/1.5 kg-PW – 7.5 kg-CO₂/7.5 kg-PW) into a single well of radial flow of uniform porosity and permeability, and that sandstone reservoirs are more suitable than carbonate reservoirs to produce H₂ by the proposed stimulation method. Simulations were conducted using our own TOUGHREACT module called CO2Bio. CO2Bio simulates the multiphase bio-geochemical reactive transport of CO₂-CH₄-H₂-H₂S mixture gases in geological carbon storage sites. To determine the effect of permeability heterogeneity on the biogenic production of H₂ by the proposed stimulation method, we incorporated permeability heterogeneity into the model consisting of a single well of radial flow. This task was achieved by measuring the permeability of four core samples of the Morrow B sandstone reservoir, and by applying a kriging geostatistical interpolation method. Simulation results indicate that heterogeneity reduces the amount of H₂ production by the proposed stimulation method, and that larger amounts of H₂ are produced in zones of high permeability than in zones of low permeability. An additional simulation was conducted placing multiple wells across the whole reservoir. After 100 days of injecting 5 kg-CO₂/5 kg-PW – 10 kg-CO₂/10 kg-PW, H₂ productions was 3,712 kg – 13,489 kg of H₂. Overall, the results indicate that biogenic H₂ production in geological carbon storage sites is feasible and a function of petrophysical, geochemical, and microbiological factors.