Oral Presentation Sub22 Conference

Carbon capture and storage (CCS) has been globally recognised as an important step towards reduction of CO2 emissions. One such CCS project is the CarbonNet in the Gippsland basin in Victoria. Measurement, monitoring and verification requirements (MMV) for CO2 geosequestration demands accurate monitoring of the CO2 plume stored in the subsurface. High resolution seismic imaging methods such as FWI (Full Waveform Inversion) can be used to efficiently monitor the CO2 plume. Successful FWI-imaging relies on data with low-frequencies and dense spatial coverage. Conventional seismic setup in offshore environments is expensive and can have a considerable environmental footprint. Fibre-optic based DAS (distributed acoustic sensing) systems can serve as a cost-efficient alternative for acquiring seismic data and can replace or supplement conventional sensors for passive and active recording.

In this study we explore the potential of using DAS as a monitoring tool to image the CO2 stored underground using both active and passive seismic imaging. Figure 1 describes an active synthetic study which uses the velocity model from the Pelican site1. Injection of CO2 leads to a drop in P wave velocity by 10 %, which can be imaged using seismic imaging methods. Synthetic shots on the water surface are modelled using elastic modelling and recorded by sensors placed on the sea-bottom. The displacement data (conventional) is undersampled in space compared to strain to reflect the capability of DAS to finely sample wavefields. In this study we avoid the conversion of DAS to displacement/velocity data by directly inverting the strain data for FWI.