Feasibility Study of Marine Controlled-Source Electromagnetic for Gas Hydrate

Natural gas hydrate is one of the most important clean energies and part of carbon cycle, due to the least carbon content. Natural gas hydrates depend on high pressure and low temperatures, located under seabed or permafrost. Small changes in temperature and pressure may lead gas hydrates to separate into water and gas, commonly as methane. As a powerful greenhouse gas, methane is much stronger than carbon dioxide. Therefore, it is necessary to detect the gas hydrates stable zone (GHSZ) before the methane gas escapes from GHSZ. Marine controlled source electromagnetic method (CSEM) is a useful tool to detect gas hydrate in offshore. The results from 3D CSEM method are a resistivity cube to describe the distribution of gas hydrates. In order to study the detectability of CSEM method, we simulate the sensitivity and resolution of marine CSEM synthetic data. By using the sensitivity and resolution, a simple statement may be quickly judged on the existence and occurrence range of the natural gas hydrate. In this paper, we compare the resolution of marine CSEM method with various transverse resistance. This information may help researchers find out whether the GHSZ exists or not.

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Computation of Apparent Resistivity from Marine Controlled-source Electromagnetic Data for Identifying the Geometric Distribution of Gas Hydrate

Geophysics and Geophysical Exploration ◽

10.7582/gge.2012.15.2.075 ◽

2012 ◽

Vol 15 (2) ◽

pp. 75-84 ◽

Cited By ~ 2

Author(s):

Kyu-Bo Noh ◽

Seo-Gi Kang ◽

Soon-Jee Seol ◽

Joong-Moo Byun

Keyword(s):

Gas Hydrate ◽

Apparent Resistivity ◽

Geometric Distribution ◽

Controlled Source ◽

Electromagnetic Data

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Offshore-onshore resistivity imaging of freshwater using a controlled-source electromagnetic method: A feasibility study

Geophysics ◽

10.1190/geo2020-0906.1 ◽

2021 ◽

Vol 86 (6) ◽

pp. E391-E405

Author(s):

Keiichi Ishizu ◽

Yasuo Ogawa

Keyword(s):

Feasibility Study ◽

Coastal Area ◽

Numerical Test ◽

Water Source ◽

Coastal Areas ◽

Depth Range ◽

Test Results ◽

Controlled Source ◽

Resistivity Imaging ◽

Model Study

Coastal freshwater provides a water source for more than one billion people living in coastal regions. For sustainable groundwater management in coastal areas, an understanding of freshwater distribution is necessary. Freshwater distribution in a coastal area can extend across the shoreline and into the offshore region. Offshore-onshore mapping of freshwater helps us to gain a comprehensive understanding of the freshwater distribution in coastal areas. Resistivity imaging using electromagnetic methods has been used to reveal the freshwater distribution in coastal areas because electrical resistivity in these settings is primarily controlled by porosity and porewater salinity. We have considered a controlled-source electromagnetic (CSEM) method for offshore-onshore resistivity imaging of freshwater at a depth range of 0–500 m below the seafloor. Our CSEM method is novel in considering an array of onshore-offshore electromagnetic receivers with onshore electric dipole transmitters. We have conducted a feasibility study to investigate the ability of the CSEM method for offshore-onshore resistivity imaging of freshwater in a coastal area. The test results indicate that the method could image the resistivity distribution of freshwater located at a depth of 500 m below the seafloor. Our model study also indicates that the offshore-onshore CSEM method can detect offshore aquifers up to 5 km from the shoreline. These numerical test results imply that our CSEM method is a promising technique for offshore-onshore resistivity imaging of freshwater in coastal areas.

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