This paper aims to research the application effect of 2.5-dimension nonlinear conjugate gradient inversion in frequency domain in the field of natural gas hydrate detection. The effectiveness of self developed 2.5 dimensional nonlinear conjugate gradient inversion algorithm has been tested through the data obtained from the South Hydrate sea area, Oregon, the United States. These data was collected through controlled source electromagnetic detection by the Scripps Institution of Oceanography in 2004. Beneath the seafloor of this area, free gas and gas hydrate have been proved to exist. Many different kinds of geophysical exploration methods have been applied within this zone. The inversion results of nonlinear conjugate gradient algorithm clearly illustrate the electrical conductivity distribution of the area 1-2 km under seafloor. The results have a remarkable meaning in the comparison research of the OCCAM inversion result for the same region. Furthermore, the details of nonlinear conjugate gradient inversion conform to the conclusions of marine magnetotelluric method, seismic reflection method, seismic sequence stratigraphy and ocean drilling programs. Therefore, the 2.5-dimension nonlinear conjugate gradient algorithm is capable of reflecting the conductivity distribution of shallow seafloor rather deliberately and exactly. This inversion method shows great potential in application, especially for small-scale reservoir, shallow buried resistivity and marine gas hydrate. |