Research On Correlation Identification And Noise Immunity Of Multi-channel Transient Electromagnetic Method

Petroleum plays an irreplaceable role in the development of a country.Meanwhile,it is also the basis of the realization of military strategy and a driving force of the economic growth.Nevertheless,China had become a net oil importer since the end of the last century,and the security of national oil is facing huge challenges.Hence,vigorously developing the technology of exploring remaining oil between wells has become an urgent task.This thesis conducts research based on the multi-channel transient electromagnetic method.Based on this method,firstly,the scaled log model was established regarding the scaled experiment method,and the error rate of the scaled model was calculated by comparing the received potentials of the original model and the scaled model,verifying the correctness of the scaled log model which is mentioned above.Secondly,the frequency spectrum of the m-sequence in the input signal of the logging model is analyzed,and the superiority of choosing m-sequence is obtained by comparing the former with the frequency spectrum of the input signal which is commonly used in the transient electromagnetic method.Moreover,the noise immunity of m-sequence based on correlation identification algorithm is analyzed.Specifically,three kinds of common noises in-field detection are added to the output signal.According to experimental results,m-sequences under different coding parameters have different anti-noise effects.Finally,two different definition methods including apparent resistivity and layered apparent resistivity at the peak moment are used to extract the resistivity of the logging model.Three sets of models are established by changing the conductivity distribution,thickness and number of layers in the model,aiming to explore the agreement between these two definition methods and the real resistivity in different situations.The results indicate that the data extracted by the layered apparent resistivity method matches the real resistivity better.Nonetheless,it has a higher error rate on the other hand;the data extracted by the apparent resistivity at the peak moment has a relatively low error rate.However,when the resistivity in a large area changes suddenly,it cannot accurately reflect the change in resistivity.Compared with the traditional electrical logging method,the multi-channel transient electromagnetic method has higher efficiency and noise resistance.It has guiding significance for the detection of remaining oil wells and is the theoretical bases for future exploration work.