| Coal mine production in China is mainly based on the operation of underground tunnels,which is affected by factors such as the geological structure of the coal seam.The geological disasters such as roof collapse,water permeability and gas outburst are prone to occur during the mining process,which seriously threatens the safety of coal mine production.Therefore,the fundamental issue of preventing disasters and ensuring safe production is how to achieve early detection of abnormal geological bodies along the coal seam in the early stage of coal seam mining and excavation.There are two aspects to summarizing application requirements:one is geosteering and the other is anomaly detection.By using the technology of LWD along the coal seam detection,it can detect the distribution of the coal seam roof and floor,faults,collapse columns and other geological hazards before mining or during the mining process.In view of the differences of application environment and design requirements between coal seam and oil formation,azimuth electromagnetic wave instrument while drilling in oil industry can not be used in coal mine.But at present,Azimuthalal electromagnetic wave logging while drilling(AELWD)detection technology and instruments are still blank in the field of coal mine.Hence,this paper deeply research the working principle of AELWD,and the detection performance of coal-rock interface.By establishing a geological model,we have mastered the instrument’s own parameters and environmental response characteristics.Based on an in-depth analysis of the effects of different coil systems and structural parameters,optimize the design of the coil system in a high-resistance coal seam environment,and then the explosion-proof small-size asymmetric orthogonal coil structure system design method in this case was proposed.For the case of strong electromagnetic noise interference in coal mines,based on the improved inverse phase change chaos detection method for Duffing oscillator to improve the detection accuracy of detection signals,which provides strong support for qualitative interpretation and instrument development in coal mines.In the second chapter,research the influence factors of electrical parameters in coal rock medium.The influence factors of coal conductivity are mainly include internal factors and external factors,the internal factors include the degree of coal metamorphism,ash and moisture,and the external factors include moisture content,temperature,dopant and geoelectric field,etc.By analyzing the influence of coal internal and external factors on the electrical characteristics of coal seam such as dielectric constant and resistivity,and based on Maxwell’s equations,established the electromagnetic wave propagation attenuation response relationship in high resistance coal seam,and grasped the influence of the internal and external factors of coal on the electromagnetic wave propagation attenuation.Using a highprecision impedance analyzer to test the dielectric constant and resistivity of coals with different metamorphisms(lignite,anthracite,gas coal,lean lean coal and long flame coal),research and analyze the relationship between coal dielectric constant with coal quality and electromagnetic wave frequency,and the relationship between resistivity with coal quality and electromagnetic wave frequency.In the third chapter,based on the theoretical research of electromagnetic logging tools,derived and got the numerical and analytical solutions of the electromagnetic wave detection response under the conditions of multi-layer parallel media isotropy and coal seam anisotropy in coal rock formations.The 3D forward modeling problem is simplified into a series of onedimensional forward modeling of layered model by simplifying the formation structure and instrument coil through dimensionality reduction,and the results of 3D numerical simulation and the dimensionality reduction fast simulation algorithm are similar,which can meet the accuracy requirement.By simulating the influence law of detection response of traditional electromagnetic waves in the high-resistance environment of coal and rock media,grasped the detection response characteristics of coal-rock layer interface,and designed a traditional electromagnetic wave instrument that can be used in high-resistance coal seams.When the coal mine application only explores the interface and does not consider the influence of orientation,this coil system design can be referred to.Through this chapter,the research on the detection response law of the traditional electromagnetic wave instrument in the high resistance coal seam will lay the foundation for the optimal design of the coil system of the AELWD in the high resistance coal seam and the study of the response law.In the fourth chapter,based on the theoretical research of azimuth electromagnetic logging tools,by comparing the detection response characteristics of different coil system structures,an asymmetric orthogonal coil system suitable for high resistance coal seams is designed.The coil system has a small size,which is not only ensure the depth of interface detection,but also meet the interface response sensitivity.By optimizing the design of the coil parameters,the coil system got the best working conditions of parameters such as frequency,source distance,and coil spacing.In this chapter,it also discusses the influence of different measurement environments in coal mines,including: instrument eccentricity,coal gangue,coal rock resistivity contrast and anisotropy,etc.Apply this coil system to the detection response simulation of low-resistance aquifers in coal seams and abnormal geological bodies found that the directional electromotive force signal of orthogonally coupled ZX components is sensitive to the changes in amplitude,which is an effective method for detecting abnormalities in coal seams.In the fifth chapter,design and development of intrinsically safe explosion-proof AELWD for underground environment of coal mine.Simulated and analyzed the detection response characteristics of directional electromotive force,optimized the structural parameters such as coil cover,drill collar,coil slot,and coil underlay to obtain the influence law of the instrument response.Through the research on the selection of intrinsically safe inductance and capacitance design parameters of the AELWD under drilling in the coal mine,established the multiple protections of voltage and current in the setting of abnormal working short circuit and open circuit.By calculating the minimum ignition energy corresponding to the capacitor voltage and inductor current in the circuit,using the improved H-bridge Buck-Boost switching regulator circuit to meet the circuit’s low output short-circuit energy,which can quickly got the maximum power point and effectively reduce circuit losses.For the traditional signal detection method,when the noise is detected,the effect of the transition zone is easily being produced by the forward phase transition.Using the inverse phase change chaos detection method combining the high-order cumulant and the Duffing oscillator,and applied the detection method to the azimuth electromagnetic wave while drilling.Weak signals can be effectively extracted during instrument signal acquisition.By testing the test well of the AELWD,the data shows that it can meet the application of high resistance coal seam. |
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