The Influence of Microbial Activities on the Capillary Pressure during H2 Injection: Implications for Underground H2 Storage

Among the several options that are being considered for reducing the concentration of carbon dioxide in the atmosphere, the steady replacement of fossil fuels with clean hydrogen stands out as the most pragmatic approach and globally recognized option. To ensure a stable supply, H-2 needs to be stored at an industrial scale due to its low volumetric energy content. Depleted hydrocarbon reservoirs are a promising choice for storing H-2 due to their high sealing properties and storage capacity. Sulfate-reducing bacteria (SRB) are usually present in depleted hydrocarbon reservoirs; however, the effects of SRB activities on the wettability of H-2/rock/SRB solution are rarely reported. Moreover, a few reported studies were conducted through contact angle measurement, but the uncertainties associated with this method limit its accuracy. Thus, this study explores capillary pressure (CP) measurements for quantifying the wettability of Berea sandstone/H-2/SRB solution. H-2/brine interfacial tension (IFT) measurement and X-ray photoelectron spectroscopy (XPS) analysis were also conducted to authenticate the CP measurement results. The CP curves for SRB-treated rocks shifted to the right, and the residual water saturation for the SRB-saturated cores was increased from 20% to 40% at 140 psi. The SRB solution did not demonstrate any significant impact on IFT values, however. The XPS analysis showed that the carboxylic acids were consumed due to the SRB microbial activity, suggesting that the relative concentration of carboxylic acid groups decreased during aging of the SRB solution resulting in significant alteration of Berea sandstone wettability toward water-wet in the presence of SRB.