Influence of Anaerobic Fermentation Parameters on In-Situ Hydrogen Production for Pressure Support in Mature Oil Wells

This study investigates microbial gas generation as a sustainable alternative for maintaining reservoir pressure in depleted oil wells through bio-based enhanced oil recovery (Bio-EOR). Conventional pressure maintenance methods, such as chemical gas injection, are often associated with high operational costs and environmental concerns. In this work, mixed anaerobic microbial cultures isolated from formation water were cultivated under simulated reservoir conditions to evaluate their capability for in situ hydrogen and carbon dioxide generation. The effects of key operational parameters, including pH (5.5–8.0), temperature (35–65 °C), and nutrient concentration using glucose as the carbon source (0.5–2.0 g L⁻¹), were systematically investigated to determine optimal gas productivity and process stability. Experimental results revealed that maximum gas production was achieved at 55 °C, pH 7.0, and 1.0 g L⁻¹ glucose, producing a gas composition of approximately 65% H₂ and 35% CO₂ with a cumulative yield of 0.84 L gas L⁻¹ culture within 7 days of incubation. Gas chromatography analysis confirmed that biohydrogen production primarily proceeded through acetate and butyrate fermentation pathways, indicating active fermentative metabolism under thermophilic conditions. Furthermore, core-flood simulation experiments demonstrated that the generated gas mixture could increase reservoir pressure by approximately 0.12 MPa day⁻¹, highlighting its potential effectiveness for biological pressure support in mature reservoirs. Overall, this study demonstrates the feasibility of microbial gas generation as a low-carbon, environmentally friendly, and cost-effective strategy for reservoir pressure maintenance and sustainable hydrocarbon recovery.