Research On Key Technologies Of Targeted Excitation With Grounded Source Of Induction-Polarization Effects Of Dual Phase Conductive Medium

With the high-quality development of the national economy,the demand for mineral resources in China is growing rapidly,leading to a prominent supply-demand contradiction.In the exploration of polymetallic deposits by time-domain electromagnetic method,as a typical multi-phase conductive medium,metal ore exhibits both induction and polarization effects,which can cause rapid attenuation and signal reversal of late electromagnetic signals.Simultaneously obtaining parameters such as resistivity and polarizability from the induction-polarization effects is of great significance for detecting and distinguishing economically valuable mineral deposits from non-profitable mineralized zones,as well as inferring and interpreting the distribution of underground mineral resources.Currently,most research focuses on electromagnetic numerical simulation and parameters inversion of the inductionpolarization effects.However,the deep induction-polarization response is extremely weak,and the sign reversal phenomenon is easily overwhelmed by noise,making it difficult to observe.Therefore,the research on targeted excitation detection methods with grounded source for the time-domain induction-polarization effects is crucial for enhancing the weak polarization response in the deep subsurface,amplifying sign reversal characteristics,and achieving high-resolution and large-depth detection of complex underground geological structures.With funding from the Key Program of the National Natural Science Foundation of China,“Research on Key Technologies of Electromagnetic Detection of InductionPolarization Symbiosis Effects of Dual Phase Conductive Medium Based on SQUID technique”,this paper focuses on the key technologies of targeted excitation with grounded source of induction-polarization effects of dual phase conductive medium.Analyzing the induced-polarization response characteristics and the coupling principle of induction-polarization effects of grounded source,designing a grounded source transmitting system for targeting excitation induction-polarization effects,and studying the method to solve the diffusion depth of induction-polarization effects can effectively improve the interpretation accuracy of induction-polarization effects and meet the requirements of domestic and refined earth exploration instruments.The main research contents are as follows:(1)Three-dimensional numerical simulation of time-domain induced-polarization electromagnetic response of grounded source based on dual-phase conductive medium.The GEMTIP model of dual phase conductive medium is designed based on the characteristics of complex multi-metal ore deposition.The three-dimensional numerical simulation of induced-polarization electromagnetic response was achieved using the three-dimensional frequency-domain finite-difference method and cosine transform method.The induced-polarization response characteristics of typical multiple metal ores were analyzed,and the influence of geometric-physical parameters of rock and ore and transmission-reception parameters on the induced-polarization electromagnetic response is studied.(2)Study on the targeted stimulation methods of induction-polarization effects of grounded source based on equivalent circuit model.The electromagnetic field analysis was transformed into circuit analysis,and an equivalent circuit model of inductionpolarization effects of grounded source was established to analyze the energy transfer process of induction-polarization effects.The concept of “optimal turn-off time” was proposed to enhance the negative phenomenon of polarization effect.The dualcontrollable trapezoidal wave excitation mode of grounded source was summarized to effectively increase induction and polarization responses.The targeted excitation relationship between induction-polarization effects and the turn-off time of the transmitting current of grounded source was established to guide the optimization of the working parameters of the grounded source transmitter.(3)Design of a high-power grounded source transmitting system with controllable turn-off time based on DC chopping technology.A 200 k W/100 A high-power grounded source transmitting system with controllable turn-off time was developed according to the detection requirements of induction-polarization effects.A method for controlling transmitting current turn-off time of grounded source based on DC chopping technology was proposed,which can continuously transmit two trapezoidal wave currents with different turn-off times to achieve targeted excitation of inductionpolarization effects.The reliability of the transmitting system was evaluated and tested,and the results met the requirements of field exploration.The effectiveness of the dualcontrollable trapezoidal wave current of grounded source for targeted excitation of induction-polarization effects was verified through an equivalent polarization ring experiment in Leshan Town,Jilin Province.(4)Multi-parameter extraction and deep imaging of induction-polarization effects based on rational function approximation algorithm.In view of the problem that the dispersion characteristics of polarization effect cause large errors in the calculation results based on traditional diffusion depth,a one-dimensional diffusion equation timedomain solution method based on frequency-domain rational function approximation algorithm was proposed to calculate the diffusion depth of induction-polarization effects and improve the interpretation accuracy of polarization medium.The extraction method for multiple parameters such as resistivity and polarizability based on quantum particle swarm optimization algorithm was studied.The field-measured data in Daxing’anling area of Heilongjiang Province and Leshan Town of Changchun City of Jilin Province,were used for multi-parameter extraction and deep imaging of inductionpolarization effects to verify the effectiveness of the method.This paper has achieved key technological advancements in the targeted excitation of the induction-polarization effects in dual phase conductive medium.The research mainly includes numerical simulation,mechanism analysis,development of the grounded source transmitter,multi-parameter depth interpretation,and experimental verification.An induction-polarization effects electromagnetic detection system of dual phase conductive medium has been established,which involves a numerical simulation of three-dimensional electromagnetic response,dual-controllable trapezoidal wave targeted excitation,multi-parameter extraction and depth imaging.This provides ideas for the precise exploration of underground deep mineral resources and the related technologies can be applied in other fields of time-domain electromagnetic exploration.