Seismic monitoring of a small CO2 injection using a multi-well DAS array: Operations and initial results of Stage 3 of the CO2CRC Otway project

Active time-lapse seismic is widely employed for monitoring CO2 geosequestration due to its ability track the distribution of fluids in space and time. However, standard 4D suffers from several challenges, including high cost, disruption other land uses, and, consequently, relatively large intervals between monitor surveys. Some these challenges can be mitigated using permanently installed sources receivers. Such an approach was tested at CO2CRC Otway site by continuous offset VSP 15,000 t supercritical injected into aquifer 1,500 m deep with nine permanent (surface orbital vibrators or SOVs) five downhole fibre-optic This complemented multi-well a mobile vibroseis source same DAS receivers, which included one baseline two surveys after injection 4,000 12,000 CO2. The DAS-SOV detected abrupt increase travel times below interval on second day (after 300 CO2) tracked growth areal plume mapping changes reflection amplitudes. also amplitudes VSPs. images obtained are broadly consistent each but some differences illumination, lateral variations velocities anisotropy. These serve as measure uncertainty images.