Marine Controlled Source Electromagnetic Methods 1-D Inversion Considering All Parameters

In recent years,the countries of the world are all facing the same problem–A shortage of resources.Exploration and subsequent utilization of the vast resources hidden under ocean floor are widely considered as one of most fruitful and promising methods available to solve this problem.Detection of the ocean resources is a prerequisite for the development of these sub-ocean deposits.However,there are significant limitations in using the traditional methods of geological exploration in an oceanic environment.Yet the advantages of applying an electromagnetic scanning method on to the seabed are obvious.The technique commonly referred to as CSEM?marine controlled source electromagnetic method?has been developed and improvements have been rapidly realized,especially with deployment in the exploration of the deep sea environment.Submarine exploration adapted with a raft of electromagnetic scanning arrays has shown miraculous results and unprecedented levels of accuracy,resolution and penetrability.The development of CSEM in China is unfortunately still in its infancy and is danger of lagging behind severely.There exists a gap between the domestic capabilities and those demonstrable on the international level.The reliability and effectiveness of the forward modeling process and developing an accurate and reliable inversion methodology are of particularly high importance for the continuing development of China's marine Controlled Source Electromagnetic Method.In the case of forward modelling simulation,it is generally assumed that only the conductivity?is changed,from the list of the medium's electromagnetic parameters?examples being,permeability,permittivity,conductivity,etc.?.The other parameters are assumed to be constants in the model,but during the actual detection these other parameters are also slightly varied.Therefore,it is a necessary requirement to study the forward numerical simulation using the full gamut of parameters and applying these protocols to investigate the accuracy of the inversion methodology.Taking a considered approach encompassing the multi-parameters of marine electromagnetic methods,will lead to noticeable advancement to the standards achievable using current practices.Applying these five principles consistently with CSEM will deliver systemic improvements.Based on Maxwell's equations,the full-parameter marine CSEM electromagnetic response formula for the frequency domain horizontal electric source in the classical one-dimensional marine geoelectric model is derived using the boundary conditions of the electromagnetic field.In the process of solving the electromagnetic field response,the Lorentz potential is first introduced and the solution under Lorentz condition is deduced.Then the solution of the Coulomb potential is obtained based on the relationship between the Coulomb potential and the Lorentz potential.For the generalized integral in the electromagnetic response formula,it is difficult to solve directly,so the fast Hankel transform is used for calculation.Based on this,a forward program was written to simulate different geoelectric models and observation systems.The OCCAM inversion method was used to compile the inversion program,and the inversion effects of different geoelectric model inversion were compared and analyzed,which provided reference for field data processing and interpretation.Get the corresponding conclusion:?1?The detection effect of the electric fieldcomponent and the magnetic fieldcomponent of the marine controlled source electromagnetic method is more significant than other electromagnetic components.?2?The forward response of marine controlled source electromagnetic method has obvious differences in depth of seawater,target layer thickness,conductivity,magnetic permeability,line position,etc.The dielectric constant has negligible influence on it.?3?The inversion results show that the marine controlled source electromagnetic method has a good inversion effect for different types of models,and it has an accurate detection effect on the buried depth,layer thickness,and resistivity range of abnormal high impedance.?4?The use of information obtained from other geological data?especially geological interface information?to constrain the inversion model can greatly improve the inversion accuracy and speed.?5?Through the analysis of the Jacobian matrix in the inversion process,the Jacobian matrix can be inverted to indicate the buried depth of the inferred geological anomaly.