Joint Inversion Interpretation Of Surface And Surface-to-underground Electromagnetic Method

The realization of fine detection of hidden water inrush disaster source in coal mine is one of the technical guarantees for safe,efficient and green mining of working face.However,at present,the transient electromagnetic method(TEM)widely used in detecting water-conducting structures in coal mines has low detection ability for deep targets,and the detection distance of mine TEM is limited.The surface-to-underground transient electromagnetic method(SUTEM),which lays a large transmitting loop on the surface and receives it in the roadway near the target body,can effectively solve the problems of weak deep detection ability of ground TEM and short detection distance of mine TEM.Because the receiving point is located in the roadway,the traditional TEM interpretation method cannot be followed.At present,this technology has not yet formed a systematic inversion interpretation method.In order to give full play to the technical advantages of SUTEM and realize fine detection,it is urgent to study the matching fine inversion interpretation method to break through the bottleneck and promote the application.In order to solve the above problems,combined with the advantages of two kinds of TEM,the SUTEM joint inversion interpretation technology is proposed,in order to realize the accurate detection of hidden water inrush disaster sources in coal mines.In this thesis,based on the theory of electromagnetic field diffusion,the forward and inversion numerical method is used as a tool to realize the accurate detection of hidden water-bearing disaster-causing factors,and the horizontal thin plate-shaped wateraccumulating goaf is used as the basic model.Combining theory with engineering practice,the joint inversion interpretation of SUTEM is carried out.The main conclusions are as follows:(1)The early induced electromotive force of TEM is less affected by the goaf of water accumulation.When 10 % is used as the abnormal response threshold,the early data does not contain the information of deep goaf.With time increases,the induced electromotive force(EMF)is affected by the goaf.When the multilayer goaves exist,the surface observation data are mainly affected by the shallow goaf;The early EMF of the SUTEM is greatly affected by the water-accumulated goaf,and the influence increases first and then decreases with time increases.The influence time is longer than that of the surface measuring point.When the multilayer goaves exist,it is mainly affected by the deep goaf.(2)Based on the vertical magnetic dipole source,the electromagnetic field component expression of the horizontal rectangular large loop at any point in the whole space is derived,and the SUTEM one-dimensional Occam joint interpretation algorithm is realized: The inversion of TEM can accurately obtain the three-layer geoelectric model information.The SUTEM is greatly affected by the middle layer,and the thickness of the middle layer increases in the inversion results;For HKH geoelectric model,TEM has higher resolution;When there are three low resistivity layers,the TEM can only accurately obtain the first low resistivity layer,and the SUTEM can obtain the position and thickness of the third low resistivity layer below the receiving point;The joint interpretation results of one-dimensional layered model are consistent with the real model,which can meet the needs of accurate detection of hidden water inrush disaster sources in coal mines.(3)The one-dimensional interpretation of TEM can obtain the location of singlelayer goaf,but there is a high resistivity area in the deep part.In the SUTEM interpretation results,the longitudinal range of single-layer goaf increases,and the resistivity above it is greater than that of the real model;In this model,the TEM interpretation cannot obtain the interface between the left and right goaves.Although the SUTEM can distinguish the top interface of the left and right double water goafs,the low resistivity area is connected below.Both explanations cannot distinguish the upper and lower double-layer water goaves.(4)One-dimensional joint interpretation has better lateral boundary resolution for single water goaf,but the longitudinal range increases;For the upper and lower doublelayer water goaves,one-dimensional joint interpretation can obtain two low resistivity regions,in which the shallow low resistivity region is close to the real model,and the vertical position of deep low resistivity region is lower than that of model design;Onedimensional joint interpretation can distinguish left and right water-accumulating goaves,and it is more obvious to describe the interface between goaves.(5)The three-dimensional joint interpretation of SUTEM is realized by multi-core CPU parallel operation and model boundary element approximation: The threedimensional interpretation eliminates the high resistivity false anomaly above and below the goaf in one-dimensional interpretation;the three-dimensional interpretation of the TEM is inaccurate in depicting the boundary of the water accumulation area.Although the location and boundary of the left and right double water accumulation goaves can be distinguished,it cannot effectively distinguish the upper and lower double water accumulation goaves;The three-dimensional interpretation of SUTEM can accurately delineate the horizontal position of the water accumulation area,but the depth positioning is insufficient.At the same time,there is a low resistivity zone above the survey line,and the boundary of the deep water-accumulation area in the upper and lower double goaves is more obvious,and the shallow goaf information cannot be obtained;The three-dimensional joint interpretation can obtain more similar interpretation results with the real geoelectric section in less iterations.It is more accurate to describe the boundary and depth of the single water accumulation goaf,and has strong resolution ability of the left and right,upper and lower double water accumulation goafs.The processing of measured data verifies the joint interpretation effect of SUTEM.The joint interpretation of TEM and SUTEM improves the interpretation accuracy of TEM detection of hidden water inrush disaster sources in coal mines.