Study Of Measures And Inversion Of The Marine Controlled-source Electromagnetic Method

Marine controlled-source electromagnetic method is a new geophysical exploration method.It has been intensively studied and successfully applied into marine hydration and gas hydrate resource detection abroad.But beginning time of this research in our country is later than aboard.Although the development of detection devices has got some process,there are still significant gaps on the aspect of data process between China and Western countries.In order to reduce those gaps,the paper presents a suit of 2.5D inversion program of marine controlled-source electromagnetic method and is based on the nonlinear conjugate gradient algorithm.Through the comparison and analysis of the influence of inversion parameters,such as regularizing operator,precondition matrix and refine factor of conjugate gradient direction,the best parameters combination is chosen and applied into the following inversion stimulation.Theoretical and measured data are used to prove the correction and effectiveness of this inversion program.The forward simulation is realized by adaptive finite element method and unstructured triangular mesh that helps to improve the program's simulation ability.Meantime,the parallel mechanism is introduced into this program that is benefit for forward calculation by division of wave numbers and frequencies.And the computing speed is also raised.Those algorithms break the limitation of 2.5D inversion that always needs server or large parallel clusters and make the 2.5D inversion could be realized on normal PC.Simultaneously,the effects and characters of deployed and towed marine control led-source electromagnetic detection method are also discussed on the basis of this 2.5D inversion program.The deployed method places the transmit dipole on the seafloor.That could help to fix the problem of absorb function of conducted seawater for weak abnormal response of small resistivity region buried shallow.This paper establishes classic geoelectric models and does some numeric calculation.Through the comparison and analysis of those numerical simulation results,the conclusion was drawn that the former method could excite greater electromagnetic response and normalized abnormal response than the latter one.And the superiority is obvious for resistivity body with thin buried sediment.And also for this kind of target,the Border resolution of deployed method was also higher than the towed method.So the deployed detection method is proper to detailed investigation in some target known area.