Use of Depleted Oil and Gas Reservoirs as Bioreactors to Produce Hydrogen and Capture Carbon Dioxide

The biological production of hydrogen offers a renewable and potentially sustainable alternative for clean energy generation. In Brazil’s Northeast, depleted oil reservoirs (DORs) present a unique opportunity to integrate biotechnology with existing fossil fuel infrastructure. These subsurface formations, rich in residual hydrocarbons (RH) and native H2 producing microbiota, can be repurposed as bioreactors for hydrogen pro-duction. This process, often referred to as “Gold Hydrogen”, involves the in situ mi-crobial conversion of RH into H2, typically via dark fermentation, and is distinct from green, blue, or grey hydrogen due to its reliance on indigenous subsurface biota and RH. Strategies include nutrient modulation and chemical additives to stimulate native hy-drogenogenic genera (Clostridium, Petrotoga, Thermotoga) or the injection of improved inocula. While this approach has potential environmental benefits, such as integrated CO₂ sequestration and minimized surface disturbance, it also presents risks, namely the production of CO₂ and H₂S, and fracturing, which require strict monitoring and miti-gation. Although infrastructure reuse reduces capital expenditures, achieving economic viability depends on overcoming significant technical, operational, and biotechnological challenges. If widely applied, this model could help decarbonize the energy sector, re-purpose legacy infrastructure, and support the global transition toward low-carbon technologies.