Experiment of marine controlled-source electromagnetic detection in a gas hydrate prospective region of the South China Sea

The purpose of this work is to test the performance of the marine controlled-source electromagnetic apparatus designed and developed by ourselves and its application in the detection of gas hydrates. Starting from the principles of the marine controlled source electromagnetic method (MCSEM), we established an ideal geo-electric model based on geological characteristics of hydrates in the test area. By carrying out the theoretical research of forward modeling and inversion calculation, we determined the technical scheme of marine controlled source electromagnetic testing. Then we utilized this apparatus and carried out the first marine electromagnetic detection in a gas hydrate prospective area of the South China Sea and collected the first batch of marine controlled-source electromagnetic data. Processing and inversion of the acquired data yielded subsurface electrical structure which differs obviously in vertical and lateral directions. Especially at the site 4, there exists an electrical resistivity layer with thickness of 50 m, top depth of 181 m and resistivity of 25 Omega m. The experiment provided valuable electrical information for the submarine gas hydrate research in this area. The results demonstrate that the instrument has reached the designed index, which marks an important step toward practicability of the marine controlled-source electromagnetic method.