Progress of transient electromagnetic detection technology for water-bearing bodies in coal mines

Geological hazards,such as goaf areas of old coal mines,roof and floor aquifers,collapse columns,karst caves,and fissures that are often encountered during coal mining have become the main hazards that endanger coal production.However,with the gradual increase in the scale and depth of coal mining,the geological conditions and observation environment have become increasingly complex,which has brought serious problems to the detection depth,accuracy,and efficiency of traditional electromagnetic methods.Effective detection of water bearing geological bodies has become a huge problem encountered in the field of coal mining.Therefore,it is urgent to innovate electromagnetic fine detection theory and technology.Transient electromagnetic (TEM) method can recover the resistivity distribution of the earth.As the water bearing bodies have big resistivity contrast with the surrounding rocks,TEM method is one of the major tools for detecting the water bearing area.This paper analyzes the research progress of TEM detection theory,method,and technology for complex structures in coal mines in recent years in China.For the theory part,the time varying point charge current carrying micro element near field theory has been introduced into the simulation of TEM method,and the underground full space electromagnetic theory has been improved with the development of numerical simulation tools.For the method part,the airborne,land based,and underground methods for near source electromagnetic detection have been developed,and a series of detection techniques suitable for airborne,land based,and underground scenarios of investigating water bearing structures in coal mines has been developed for general and detailed investigations.It is pointed out that transient electromagnetic multi resolution method,big data technology,fine detection technology of multi layer coal mine goaf and the research and development of transient electromagnetic high resolution data acquisition equipment are the research directions for detecting complex water bearing bodies in coal mines.