Combining Marine Electromagnetic and High Resolution Seismic Imaging: Application to Shallow Gassy Environment

Flamme, J.; Fabre, M.; Tarits, Pascal; Marsset, Bruno; Lepot, A.

doi:10.4133/sageep.32-077

Cited by 1 publication

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“…The velocity and resistivity were coupled by a gradient correlation (Flamme et al., 2019). We added a coupling term between resistivity and velocity ( S ) in the cost function (Equation (2)).…”

Section: Methodsmentioning

confidence: 99%

Characterization of gas‐bearing sediments in the coastal environment using geophysical and geotechnical data

Dusart

Tarits

Fabre

et al. 2022

Near Surface Geophysics

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Seismic investigation in marine gas-bearing sediments fails to get information below the acoustic mask created by free gas. To circumvent this problem, we combined collocated multichannel ultra-high resolution seismic imaging, marine electrical resistivity tomography (MERT) and core sampling to study the physical properties of gas-bearing sediments in the Bay of Concarneau (France). We obtained sections of compression (P-) wave velocitvalues where free gas was identified in seismic data. We tested a joint processing workflow combining the 1D inversion of the MERT data with the 2D P-wave velocity through a structural coupling between resistivity and velocity. We obtained a series of 2D resistivity models fitting the data whilst in agreement with. The resulting models showed the continuity of the geological units below the acoustic gas fronts which is associated with paleo-valley sediment infilling. We were able to demonstrate relationships between resistivity and velocity differing from superficial to deeper sediments. We established these relationships at the geophysical scale then compared the results to data from core sampliand porosity). We inferred the porosity distribution from the MERT data. At the core locations, we observed a good agreement between this geophysical scale porosity and the core data both within and outside the gas-bearing sediments. This agreement demonstrated that resistivity could be used as a proxy for porosity where no was available below gas caps. In these regions, the observed low resistivity showed a high porosity (60-70%) down to about 10-20 m in depth in contrast with the surrounding medium with porosity less than 55%. These results support the hypothesis that failures inside the paleo-valley sediment could control the gas migration

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Section: Methodsmentioning

confidence: 99%