Comparative study on hydrogen losses via microbial byproduct in the presence of methane and nitrogen cushion gas

This study comprehensively investigates H₂ loss resulting from injecting two gas mixtures: I (60% H₂ + 30% CH₄ + 5% N₂ + 5% CO₂) and II (60% H₂ + 30% N₂ + 5% CH₄ + 5% CO₂) into an aqueous solution containing 20,000 ppm sodium chloride and 100 ppm acetic acid (a microbial by-product of acetogenesis) within Bandera clay-rich sandstone reservoirs. Conducted at 42 °C and 1350 psi, various analytical techniques, including X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, porosity and permeability assessments, pH and ion analysis, and gas chromatography, were utilized to assess the relevant properties of rocks, formation water, and gas content before and after 50 days treatment. The results indicate minimal sample reactivity, with dissolution primarily affecting dolomite and albite minerals. On average, porosity increased by 19% in formulation I and 15% in formulation II, while permeability decreased by 4.7% in formulation I and 5.3% in formulation II. In formulation I, H₂ fraction decreased by 2.79%, CH₄ increased by 7.15%, and CO₂ decreased by 9.36%, with N₂ remaining constant, whereas in formulation II, H₂ only decreased by 1.3%, CH₄ increased by 19.22%, and CO₂ decreased by 3.58%, with N₂ remaining consistent. Overall, the N₂ cushion gas condition (i.e., formulation II) slightly outperformed CH₄ in minimizing H₂ losses. This study thus provides significant insights into potential H₂ loss within a microbial-by-product-rich environment for underground hydrogen storage.