Applied technologies and new advances of parallel electrical method in mining geophysics

Parallel Electrical Method ( PEM) is a kind of geoelectric field exploration method,which integrates the synchronous acquisition and processing of whole array,all electrodes,all waveforms and three kinds of electric fields. It takes the parallel measurement and parallel processing of geoelectric field in both space and time domain as its core idea based on the integration of an ADC and a switch device for each electrode,the parallel excitation and acquisition of all electrodes are realized,and the geoelectric data volume is obtained containing AM mode and ABM mode. Ac- cording to the space combination and time series of electrodes,the excitation current sequence and potential response sequence of natural electric field ( zero field),excitation electric field ( primary field) and induction electric field (secondary field) are decomposed,and thus the resistance properties (including self-potential,resistivity and polariz- ability etc. ) of the detecting medium are analyzed according to the transmission principle of potential response and current excitation,therefore,the parallel analysis of three kinds of electric field information is realized using this meth- od. The Mine-PEM makes full use of roadway space,borehole space and its combination form in coal mine,thus it can effectively explore water-filled source,water-bearing fault,karst collapse column and grouting effect in both roof and floor,dynamically detect mining rock damage characteristics and water-rich anomaly area,real-timely monitor groundw- ater seepage evolution and predict mine water disasters. In the past 15 years,these techniques have been widely ap- plied and promoted in coal mine water disaster prevention all over China,as a result of which the technology system of Mine-PEM has been established. The intelligent characteristics of Network Parallel Electrical Method show its advanta- ges thanks to the popularization of Internet of Things technology in coal mines in China,which realizes the online re- mote control of timing excitation and acquisition as well as real-time dynamic monitoring of mine geoelectric field. Fur- thermore,the Double-mode Electrode Testing Technique overcomes the shortcomings of using the same electrode for both excitation and acquisition in normal geoelectric measuring techniques,such as multi-electrode resistivity method (high-density electrical method),which always results in errors or even failures with natural electric field and induced electric field data,and this technique ensures the data validity of PEM. Therefore,the PEM effectively integrates active source exploration and passive source monitoring,which makes a significant contribution to the dynamic and fine de- tection of mine disaster sources,especially to mine water hazards early-warning,and presently two Chinese energy in- dustry standards closely related to PEM has been implemented. Additionally,PEM not only provides a technical sup- port for intelligent mines and transparent mines construction in China,but also has been widely used in engineering ge- ophysics,environmental geophysics and urban underground space exploration areas. At present,the parallel analysis and joint inversion of multi-parameters of geoelectric field is the key research area of PEM,and by studying the elec- tric impedance tomography theory based on PEM,effective means should be formed to explore multi-field coupling and evolution characteristics in multi-phase media.