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., CO 2 ) 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 CO 2 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 CO 2 bubble plume with a gas flux rate of 2.3 L/min at ranges of up to 8 m, and determining gas flux and bubble size accurately at ranges of up to 4 m in shallow water, where the bubble sound pressure is 10 dB above that of the ambient noise.

Passive acoustic localisation of undersea gas seeps using beamforming

“…Typical underwater acoustic propagation channels contain characterised as multipaths, e.g. assumed to be reflections from the sea surface and seafloor, propagation in the seabed, and refraction in the water column due to the depth-dependent sound speed profile (SSP) Li et al (2016); ; Li (2017); Li et al (2020). Thus a simplification of spherical spreading of the bubble sound radiated from the seafloor may not be accurate.…”

Quantitatively Monitoring Bubble-Flow at a Seep Site Offshore Oregon: Field Trials and Methodological Advances for Parallel Optical and Hydroacoustical Measurements

“…These are, however, limited (by the range of visual observation) to a distance of a few meters, making active acoustic approaches in combination with optical observatories the method of choice for the quantification of bubble emissions of large areas. Alternatively, passive acoustics has emerged as a new supporting technique for quantitative monitoring of seep areas, including CO 2 CCS areas (Bergès et al, 2015;Li et al, 2020a;Longo et al, 2021;Caudron et al, 2022). Moreover, the combination of hydroacoustics and optical techniques has also been used for studying the dissolution of bubbles within the water column, including the validation of models for mass transfer and bubble transport for natural bubble seepage (Wang et al, 2020).…”

Efficient marine environmental characterisation to support monitoring of geological CO2 storage

“…formation of authigenic carbonates/bacterial mats and other typical fauna, pockmark formation, bubble release or black (sulfidic) sediments (Judd and Hovland, 1992). Passive acoustic methods have shown promise for detection and possibly quantification of gas bubbles (Berges et al, 2015;Li et al, 2020), by recording the acoustic signature of bubble release and bubble size. Knowledge of the presence or absence of natural biogenic and…”