Comparing simultaneous methods of gas flux quantification, offshore Panarea, Mediterranean Sea
Abstract
With the expected large scale adoption of carbon capture storage, a growing importance has been placed on developing methods for the accurate detection and quantification of gas flow across the seabed, in order to provide long term monitoring systems. Passive acoustic gas flux inversion has a huge potential to fulfil this role as it is low energy, low cost and capable of operating over extended periods.
Passive acoustic gas flux inversion relies on the distinct acoustic signature emitted by a bubble when it escapes from sediment into the water column, which is dependent on their equilibrium radius. Detecting and sizing individual bubbles from their natural resonance frequency is straightforward. At higher flux seeps signals overlap and we must instead consider the acoustic emissions from numerous bubbles with a range of bubble sizes. Thus by inverting an audio recording of a gas seep we are able to derive the spectral generation rate of bubbles, i.e. the rate at which bubbles of different sizes are being released, thus determining the gas flux at any given ebullition site. Despite extensive laboratory testing there has been relatively little quantitative comparison of natural gas flux made via passive acoustic inversion to those made with other more traditional techniques, i.e. direct physical measurement and optical. We designed and built a specialist acoustic optical seabed lander capable of collecting simultaneous acoustic and optical data alongside physical diver measurements. It was deployed offshore Panarea (Italy), a shallow marine environment, known for its range of natural CO 2 seeps resulting from underlying magmatic degassing. In this presentation, by actively comparing synchronised datasets from four seeps with differing ebullition characteristics, we will demonstrate that passive acoustic gas flux inversion produces results that are reliably consistent with other traditional techniques but with greater efficiency.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S31E0575R
- Keywords:
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- 0599 General or miscellaneous;
- COMPUTATIONAL GEOPHYSICS;
- 0999 General or miscellaneous;
- EXPLORATION GEOPHYSICS;
- 7290 Computational seismology;
- SEISMOLOGY;
- 7299 General or miscellaneous;
- SEISMOLOGY