Passive acoustic monitoring of a natural CO₂ seep site - implications for carbon capture and storage

Abstract

Estimating the range at which an acoustic receiver can detect greenhouse gas (e.g., CO2) leakage from the sub-seabed is essential for determining whether passive acoustic techniques can be an effective environmental monitoring tool above marine carbon storage sites. Here we report results from a shallow water experiment completed offshore the island of Panarea, Sicily, at a natural CO2 vent site, where the ability of passive acoustics to detect and quantify gas flux was determined at different distances. Cross-correlation methods determined the time of arrival for different travel paths which were confirmed by acoustic modelling. We develop an approach to quantify vent bubble size and gas flux. Inversion of the acoustic data was completed using the modelled impulse response to provide equivalent propagation ranges rather than physical ranges. The results show that our approach is capable of detecting a CO2 bubble plume with a gas flux rate of 2.3L/min at ranges of up to 8m, and determining gas flux and bubble size accurately at ranges of up to 4m in shallow water, where the bubble sound pressure is 10dB above that of the ambient noise.

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Identifiers

ORCID for Jianghui Li: orcid.org/0000-0002-2956-5940

ORCID for Ben Roche: orcid.org/0000-0002-0730-2947

ORCID for Jonathan Bull: orcid.org/0000-0003-3373-5807

ORCID for Paul White: orcid.org/0000-0002-4787-8713

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