Numerical experiments on hydrogen storage characterization in porous media using elastic full-waveform inversion

Abstract In recent years, underground hydrogen storage (UHS) has garnered significant attention as a concept for large-scale energy storage. Developing hydrogen characterization and monitoring methods specific to each target geologic formation (e.g., salt caverns, reservoirs in depleted oil/gas fields, and saline aquifers in porous media) is crucial for the safe operation of hydrogen storage. However, due to the limited number of actual operations and laboratory experiments (e.g., rock physics for hydrogen) related to UHS in porous media, the specifications required for seismic monitoring (e.g., P-/S-wave velocity and density changes generated by hydrogen injection) are not yet fully understood. A recent study showed the results of laboratory experiments on cyclic UHS in porous media. The experiments demonstrated that P-wave velocity decreases nonlinearly with increasing hydrogen saturation in sandstone specimens, with a reduction of up to 3.5% observed at 36% hydrogen saturation. This study presents hydrogen characterization in porous media with conditions similar to the experiment using elastic full-waveform inversion (FWI) for time-lapse surface seismic data. The shot data are generated by seismic forward modeling for several synthetic subsurface models that incorporate a hydrogen plume. The hydrogen plume assumes four velocity-density scenarios, partially based on the laboratory study results. Numerical experiments are conducted to explore the validity and challenges of hydrogen characterization using elastic FWI.