Transport and microbial controls on subsurface hydrogen methanation revealed by microfluidic experiments and simulation

Geomethanation, the in situ conversion of hydrogen and carbon dioxide into methane through the microbial activity of methanogens within geological formations, remains a promising technology for simultaneous carbon dioxide utilization, hydrogen storage, and natural gas production. Despite interest in this process, uncertainties persist regarding the efficiency of the conversion process and its competitiveness for subsurface space, particularly given the increasing demand for hydrogen storage and carbon sequestration. Detailed knowledge of relevant reservoirs, combined with laboratory testing, is needed to evaluate the potential of subsurface environments for hydrogen methanation. Several factors, such as substrate availability and the supply and presence of essential nutrients in brine, govern microbial growth and conversion efficiency. We developed a coupled experimental–numerical approach that combines a novel high-resolution microfluidic platform with direct numerical simulations to resolve mass transfer and methane production kinetics at the pore scale. The workflow includes micromodel colonization, anaerobic introduction of substrates, and gas analysis via chromatography measurements. A microfluidic reactor setup was used to investigate biomass distribution and gas dynamics and to calibrate the numerically determined results, which may have significant implications for gas conversion and recovery. (1) During substrate gas injection, microbial aggregation shifted from a colony-dominated lifestyle to a planktonic lifestyle. (2) The observed colony disintegration and cell migration toward gas–liquid interfaces may support substrate uptake and conversion efficiency. The experiments yielded a methane evolution rate, peaking at ∼ 0 . 35 mmol/Lh. (3) Dimensionless analysis revealed distinct transport regimes within the pore network, ranging from molecular diffusion to advective mixing. These findings demonstrate that a balance among microbial activity, interfacial mass transfer, and advective nutrient supply governs the geomethanation process in unsaturated flow environments.