Data Processing Of Marine Controlled Source Electromagnetic Based On Deployed Transmitting

In recent years,with the increasing demand for marine resources and the decrease of onshore oil and gas resources and reserves,the artificial source electromagnetic method has been used in the field of marine exploration and achieved good results.In recent ten years,China has also carried out scientific research on the marine electromagnetic method,including theoretical research,independent research and development of instruments,etc.,but compared with the international relatively mature technology,the application of the marine controllable source electromagnetic method in China still needs to be improved.This paper relies on the national special project-exploration project of natural gas hydrate resources in the sea area,this paper makes a deep research on the data processing of the marine controlled source electromagnetic method based on deployed transmitting.Different from the traditional towed transmitting mode,the deployed transmitter is connected and placed on the seabed by a deep streamer,and the transmitting electrode is composed of two sets of orthogonal antennas.The electromagnetic signal is transmitted by the way of alternating transmission close to the seabed.Compared with the towed electromagnetic signal,excitation on the sea floor can greatly reduce the attenuation of the signal in the sea water,improve the quality of the source signal and the signal-to-noise ratio of the received signal.Because of the nature of its orthogonal source,the transmitted signal is excited from two different directions,and the electromagnetic receiver located in the seabed can receive multicomponent electromagnetic signal which more fully reflects the geological structure of the seabed,and to a certain extent,it weakens the multi-resolution of inversion.In this paper,the data processing method of controlled source electromagnetic method based on deployed transmitting is introduced,in which the data preprocessing method is the main method.In the pre-processing stage,the main steps are data reading and correction,filtering and de-noising,data superposition,time-frequency conversion,normalization,calculation of rotation invariants and rapid imaging of apparent resistivity.Finally,the inversion calculation of sea trial data is carried out through one-dimensional Occam inversion program to comprehensively interpret geological structure information.One dimensional high resistivity layer and two-dimensional high resistivity body models are established successively,forward simulation data are generated,and algorithm calculation is substituted.The results show that the algorithm is relatively stable and has certain practical value,especially in the aspect of apparent resistivity rapid imaging,it can get the abnormal shape and distribution of high resistivity body in a very short time,which greatly reduces the calculation cost to a certain extent.In 2015,the project team carried out the ocean test of controlled source electromagnetic method in the way of deployed transmitting,and acquired the measured data of 6 transmitting points and 4 receiving points in a sea area of South China Sea.The pseudo section of apparent resistivity is obtained by substituting the measured data into the preprocessing algorithm,and one-dimensional Occam inversion is carried out.The calculation results show that the rapid imaging results of component apparent resistivity will lead to a certain "false anomaly",while the section of apparent resistivity based on rotation invariants is similar to the one-dimensional inversion anomaly to some extent,and the pseudo section of apparent resistivity can show the ground.The result of inversion can read the magnitude and depth of ground resistivity quantitatively.