Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

High resolution calibration of seismic data with pore water data - tool to estimate gas fluxes directly from seismic measurements

Introduction of the result:
Methane - a green house gas of major importance – is often present in marine sediments in concentrations exceeding saturation. In these environments methane exists as free gas, which occupies the sediment as gas bubbles. Gas bubbles are impenetrable to sound waves, which are therefore, reflected when they are aimed into the sediment and hit methane gas. Therefore, a seismic survey (i.e. sound waves penetrating into the sediment) may reveal the depth of methane saturation if methane is present.

Result description:
Seismic surveys show the methane saturation depth with a resolution of about 25cm or better for approx. each 60 cm across the seafloor given a shooting range of 4 s-1 and a speed of 4.5 knots. Thus the methane saturation depth in large areas of the sea floor may be monitored by seismic surveys not only within a relatively short period of time and but also with a very detailed depth and area resolution compared to sediment sampling which is both time consuming and costly. Furthermore, due to the pressure release during sediment retrieval, methane is lost from the sediment and true in situ concentrations of methane saturation are therefore difficult to determine.

Key innovative features/ key findings:
There is a linear correlation (R2=0.881) between the depth of methane saturation measured by seismic survey and sediment sampling. At 20-36 m water depth, methane net oxidation is linearly correlated (R2=0.743) with methane saturation depth. Hence, with these prerequisites it is possible to estimate methane net oxidation by seismic survey, alone.

Current status & use:
The seismic survey method is under development and statistical analysis of the seismic signals obtained during the project are currently performed.

Dissemination & use potential:
The seismic survey will be useful to uncover areas of the sea floor with elevated concentrations of methane gas. The depth of methane saturation may reveal hot spots in the marine environment if methane oxidation predominates close to the sea floor, which implies high production of toxic hydrogen sulfide and thus oxygen consumption.

Thus ultimately seismic survey may also be used to spot areas of the sea floor where oxygen depletion may initiate. The method therefore appeals to environmental management strategies but will also be useful in scientific projects dealing with methane and reduced sediments (i.e. within the ERA-NET BONUS).

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Vejlsøvej 25
8600 Silkeborg
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