Understanding potential leakage pathways is critical for safe geological CO2 storage, with faults representing one of the main risks. To investigate CO2 migration through a shallow fault and test monitoring strategies, CO2CRC’s Otway International Test Centre injected ~16-tonnes of CO2 gas at a depth of ~80 m over 8 days. Traditional time-lapse seismic methods that are effective for monitoring deep storage are impractical for rapid monitoring over daily timescales, given the fast plume movement. Instead, the injection was monitored with 4D reverse vertical seismic profiling (RVSP), with a borehole source and a dense pre-installed array of 3400 surface geophones spaced on a 2.5 × 2.5 m grid. RVSP was complemented by cross-hole measurements with the same sparker source and distributed acoustic sensors in a nearby injection well. The results reveal two time-lapse velocity anomalies, one at the injection depth and another much shallower, confirming upward CO2 migration. While 4D RVSP gives a 4D image of the plume, cross-hole results are limited to a 2D plane, but give higher spatial resolution and can be repeated for long-term monitoring, revealing further upward migration of CO2.
Tertyshnikov et al. (Wed,) studied this question.