Effect of methylene blue on wetting characteristics of quartz/H2/brine systems: Implication for hydrogen geological storage

Hydrogen (H2) is considered a promising replacement for fossil fuels due to its enormous potential as an envi-ronmentally friendly and sustainable option compared to carbon-based fossil fuels. However, storing the vast quantity of H2 required to satisfy the global energy demand on the earth's surface can be difficult due to its compressibility and volatility. The best option for large-scale storage is underground H2 storage (UHS), which can be retrieved when needed. Rock wettability is vital in UHS because it determines the H2 storage capacity, containment security, and potential withdrawal and injection rates. Organic acid inherent in storage formations could make the storage rock H2-wet and reduce the residually trapped H2; thus, recent research efforts have concentrated on modifying sandstone formations contaminated with organic acid through chemical injections, such as nanofluids and methyl orange. However, previous research has not considered applying methylene blue (MB) as a rock wettability modifier to promote successful UHS. In addition, MB is a toxic constituent of wastewater, causing pollution. This research aims to dispose of MB in underground reservoirs to alter the wettability and increase the H2 storage capacity, mitigating anthropogenic carbon dioxide emissions. We assess the application of MB as a chemical agent for altering the wettability of quartz contaminated with stearic acid to promote H2 geological storage. Based on the contact-angle measurements, quartz aged with the optimum con-centration of MB (100 mg/L) has the least advancing (& theta;a = 35 degrees), and receding (& theta;r = 32 degrees) angles at 13 MPa and 50 degrees C, changing the wettability to strongly water-wet. We demonstrate that an injection of MB into geological formations could make the rock water-wet, promoting H2 containment security and assisting in the large-scale implementation of UHS.