Research On MT Noise Denoising Method And Test Platform In Marine Controlled-source Electromagnetic Exploration

With the land resources drying up,many oil companies have turned their attention to the ocean.Marine controlled source electromagnetic(MCSEM)exploration is a new geophysical detection method which can effectively identify the high resistivity reservoirs and improve the success rate of drilling.Signal denoising is an important part of data processing in MCSEM.When the distance between transmitters and receivers are medium or long,the magneto telluric(MT)signal is one of the main noise that affects the MCSEM inversion quality.However,there are relatively few studies about the processing of MT signal interference at home and abroad.At the same time,there is no suitable evaluation criterion to assess the effectiveness of the existing MT noise reduction methods.In order to solve the above problems,this thesis has studied the MT noise denoising methods and test platform in MCSEM and finished the following work.Firstly,in order to obtain the appropriate simulation data in the MT noise reduction experiment,this thesis carries out one-dimensional forwarding for signals and noises.At the same time,the input parameters of the forward modeling are analyzed.In particular,the effects of different transmitting modes,transmitting frequencies and thickness of oil and gas reservoirs on the electromagnetic response of MCSEM are studied.Secondly,considering that MT noise has great influence on MCSEM signal and there are relatively few researches on MT noise reduction,the data of MCSEM and MT one-dimensional forwarding are used to study the MT noise reduction methods based on doubly symmetric transmitting waveform,short-time window combined with pre-whitening filtering and sparse decomposition in this thesis.The results of numerical simulation show that the above methods can effectively remove the influence of MT noise and improve the signal-to-noise ratio of MCSEM signal.Thirdly,in order to study the effects of different transmitting modes,frequency combinations and iterations on the inversion accuracy,one-dimensional OCCAM algorithm is used to analyze the above influencing factors and the substantive conclusion is obtained through the simulation experiment,which can provide constructive suggestions for the inversion of the real data.Finally,the effectiveness of MT noise denoising methods needs to be verified due to the lack of quantitative evaluation of noise reduction effects.In order to solve the problem,this thesis designs a test platform by combining one-dimensional forwarding for signals and noises,noise reduction processing and one-dimensional resistivity inversion.The mean square relative error between the resistivity inversion results and the input values of the resistivity is adopted as the quantitative evaluation parameter to evaluating the denoising effect in the test platform.The simulation and real data processing are used to verify the effectiveness of the above three denosing methods by the platform which can also be generalized to the quantitative evaluation of the reduction effectiveness of other type noises...