Research On Key Technologies And Principles Prototype Of Borehole Logging Radar

Based on the original research of the research team,the key technologies of the subsystems of borehole logging imaging radar,such as time-domain signal source,time-domain antenna,microwave and control circuit,data acquisition and imaging algorithm,are systematically studied.A prototype of borehole logging imaging radar based on impulse system is designed and developed.Experiments are carried out in test wells,and the test results meet the expected requirements.Aiming at improving peak power of time-domain signal source,reducing trigger jitter,reducing electromagnetic radiation interference of time-domain signal source and shaping pulse waveform,the application foundation and experimental analysis are carried out.A time-domain signal source based on solid-state fast switching device(avalanche transistor)and Marx circuit are designed and developed.Peak voltage 500 V,peak-peak pulse width 0.5 ns(bipolar pulse waveform),repetition frequency 1-50 kHz adjustable,amplitude jitter 1.1%,root mean square time jitter 30 ps.Aiming at the specific application environment of oil drilling and the technical requirements of broadband matching,miniaturization,high radiation efficiency,high fidelity of waveform,tail signal suppression,omnidirectional transmission and directional reception of time domain antenna design,etc,an improved dipole omnidirectional transmitting antenna and a directional radiation receiving antenna based on resistance loading are designed and developed by combining simulation with experiment;The bandwidth of receiving and transmitting antennas is 0.3-2.5 GHz and the time domain gain is 3 dBi,the range of impedance varies from 40 to 60Ω,the waveform fidelity factor is 95%,an amplitude ratio of main signal to trailing signal is10:1,and the duration of trailing signal of less than 2 ns;Time-domain pattern of E-plane and H-plane of transmitting antenna are±35°and±180°,respectively.The geometric dimensions of the antenna is 50×2×0.15 cm~3,time-domain pattern of E-plane and H-plane of receiving antenna are±35°and±60°respectively,peak power ratio is36:1,the geometric size of antenna isΦ6.8×18 cm~3.Using equivalent sampling and embedded time-control circuit technology,the time control and receiving front-end circuit subsystem with the bandwidth is 0.3-2.5 GHz,the gain is 10-60 dB and adjustable,the ADC resolution is 16 bits,the sampling rate is6 GHz,the delay precision is 250 ps,the trigger time jitter is 10 ps,the delay range is300 ns,the repetition frequency is 1-50 KHz and adjustable,the controllable signal branch number is 10 channels,and the geometric size is 12×8×3 cm~3,is designed and developed.Based on the characteristic timing points of receiving and transmitting antenna direct wave signals,an imaging algorithm is proposed,which uses time alignment,amplitude normalization,accumulated average noise reduction of signals,digital filtering and time-varying amplification step by step.Clear target imaging images are obtained in laboratory and experimental well testing.Based on the research of software and hardware of each subsystem,a prototype system of borehole logging radar with geometric size isΦ9×300 cm~3 and real-time imaging is developed.The test data show that the detection distance of the prototype system is 3-15 m,the range resolution is≤10 cm,the angular resolution is≤±5°,and the temperature adaptation range is-40-80℃.The development of principle prototype has accumulated technical and experimental data for further engineering prototype development,which is expected to meet the urgent needs of the crack detection equipment in the process of shale gas exploitation.