In-Situ Hydrogen Generation from Kerogen-Bearing Reservoirs Using Microwave-Assisted In-Situ Combustion

Abstract Hydrogen is a promising low-carbon energy carrier; however, conventional hydrogen production methods are energy intensive and face significant challenges related to storage and transportation. This study investigates the potential for in-situ hydrogen generation from hydrocarbons using in-situ combustion (ISC), with particular emphasis on the role of kerogen content and heating mode. The objective is to evaluate whether hydrocarbon reservoirs can function as integrated subsurface hydrogen generation systems while minimizing surface energy input and storage requirements. A total of ten combustion experiments were conducted using rocks and fluids from the Bakken Formation. Conventional ISC and microwave-assisted combustion experiments were performed using kerogen-rich source rock, kerogen-poor reservoir rock, and controlled mixtures of the two under identical oil–brine saturation conditions. Microwave-assisted experiments employed a customized quartz-tube reactor with continuous air injection, while gas compositions were quantified using gas chromatography. The effects of kerogen abundance, heating rate, and mineralogical composition on temperature evolution and hydrogen yield were systematically evaluated. Results show that microwave-assisted combustion significantly outperforms conventional ISC in terms of hydrogen generation, even when similar peak temperatures are achieved. The enhanced hydrogen yield is attributed to the substantially higher heating rates produced by microwave stimulation, which favor abrupt hydrocarbon and kerogen cracking, reforming, and gasification reactions. Hydrogen yield generally increased with increasing kerogen content; however, temperature response did not scale monotonically with kerogen abundance. Instead, maximum temperatures were observed at intermediate mixtures of kerogen-rich and kerogen-poor rocks, highlighting the importance of mineralogical interactions, particularly between clay-rich and carbonate-rich phases, in microwave energy absorption. Rock-only experiments produced minimal hydrogen, demonstrating that hydrogen generation arises from coupled reactions involving kerogen, crude oil, and formation brine. This study provides the first systematic experimental comparison of conventional and microwave-assisted ISC for hydrogen generation from kerogen-bearing reservoir systems. The results demonstrate that subsurface hydrocarbon reservoirs can serve as in-situ hydrogen generators, with the added potential for underground hydrogen storage and retention of carbon-bearing gases, offering a novel and energy-efficient pathway for low-carbon hydrogen production.