Wave-Induced Fluid Flow as an Indicator of Biofilm Growth and Containment of Underground Hydrogen Storage

Underground hydrogen storage (UHS) is central to balancing renewable energy supply and demand, yet its reliability is threatened by biogeochemical reactions driven by hydrogenotrophic microorganisms. These microbes consume hydrogen and stimulate corrosion, mineral precipitation, and biofilm formation - all of which degrade reservoir performance and injectivity.

Seismic monitoring is a standard tool for tracking such processes at reservoir scale. This project studies the sensitivity of seismic methods to such transformations due to wave-induced fluid flow (WIFF) effects. The presence of H2 in the pore space as well as polymeric biofilms modify effective pore-fluid viscosity and compressibility, which may potentially alter seismic velocity and attenuation. We conduct laboratory tests and digital rock physics estimate the impact of two  main WIFF processes: grain-scale squirt flow and mesoscale patchy saturation.

Sandstone core samples are incubated under anaerobic conditions with sulfate-reducing and aerobic bacteria and characterized using SEM, μCT, Raman spectroscopy, and chemical assays to quantify biomass and mineral alteration. Ultrasonic transmission (500 kHz–1 MHz) tracks the evolution of the seismic properties and relates them to the petrophysical and microbial time-lapse measurements. At a much lower frequency range (~1 kHz), Split Hopkinson Resonant Bar measurements capture seismic responses across frequency bands relevant to borehole seismic monitoring at field scale.

Our measurements show a typical Gassmann-type behaviour of the seismic velocities with H2 saturation. Also, we found a very clear dependence of the seismic attenuation on the size of gas bubbles due to acoustic resonances of the gas patches. However, our study confirmed that injection of H2 gas into a reservoir that already contains another gas (either a depleted hydrocarbon play or a cushion gas) produces changes that are below standard seismic methods. At the same time, leakage of H2 to a fully brine-saturated formation can be confidently detected even for very small volumes.

On the other hand, our measurements suggest that viscous polymeric films may be able to detect microbial activity during hydrogen storage. Thus, seismic might be an effective tool to ensure UHS security while addressing fundamental questions of coupled fluid–rock–microbe dynamics.