矿井巷道-钻孔瞬变电磁二维拟地震反演方法及应用

采空巷道严重威胁煤矿安全和矿工生命,因其体积规模较小,常规物探对其探测精度较差,钻探手段也很难准确命中目标,为解决采空巷道的精细探测问题,提出一种煤矿井下巷道-钻孔瞬变电磁探测方法。该方法属于一种定源动接收的二维工作方法,通过在孔口布设一固定不动的发射线框,在孔内沿钻孔移动接收探头进行三分量观测,进而实现对钻孔径向低阻地质异常体的高精度探测。该装置观测曲线形态复杂,反演难度大。通过基于CPU+GPU异步并行的时域有限差分三维数值模拟分析了其数据特征,提出了结合分时段和全时段波场反变换算法2者优势的基于相关的滑动时窗波场反变换算法对数据进行高精度波场转换,研究了二维装置的虚拟波场时距曲线特征,得出了相应的动校正算法,采用等效导电平面法构建了初始速度模型,最终在虚拟声波介质假设下通过共轭梯度全波形反演技术实现了巷道-钻孔瞬变电磁数据的拟地震反演。计算了三维数值模拟、水槽物理模拟和井下现场模拟资料的反演结果,对钻孔径向的小规模异常体取得了良好的成像效果。结合山西煤矿井下的工程实践,对该方法精细探测积水采空巷道性质、形态和规模的实用性和有效性进行了检验。研究表明:巷道-钻孔瞬变电磁探测方法是井下物探与钻探的有机结合与相互补充,能够有效应用于积水采空巷道探测。

Method and application on 2D pseudo-seismic inversion of Roadway-Borehole transient electromagnetic detection in coal mine

Goaf roadway poses a vital threat to coal mine safety and miner’s life.The scale of the goaf roadway volume is relatively small,therefore,the ordinary geophysical prospecting method can hardly detect it accurately.Also,the drilling method can rarely hit the target precisely.For the purpose of detecting the goaf roadway more precisely,a roadway-borehole transient electromagnetic method(TEM),belonging to a 2D operating method with fixed source and dynamic reception device,was proposed.This method,by arranging a fixed transmission cable over the borehole and shifting a receiving probe along the borehole to implement three-component observation,realized a high-precision detection for the borehole radial geological anomalous bodies.The device,with more complex observation curve,had harder inversion difficulties.By analyzing the data characteristics adopting asynchronous parallel GPU plus CPU finite-different time-domain 3D numerical simulation method,this paper presented a related sliding time window wave-field inverse transformation algorithm,combined the both advantages of time segmentation and full time wave-field transformation algorithm,to transform data with higher accuracy.By studying the characteristics of time-distance curve of 2D transient electromagnetic virtual wave field data,a corresponding dynamic correction algorithm was derived.By adopting equivalent conductive plane method,initial velocity model was constructed.Ultimately,based on virtual acoustic medium hypothesis,the roadway-borehole TEM data pseudo-seismic inversion was realized by the means of conjugate gradient full-waveform inversion technique.The inversion results of 3D numerical simulation,flume simulation experiment and coalmine on-site simulation data showed that it had acquired favorable effect in exploring small-scale anomalous body on the radial direction of the borehole.In order to test the practicability and availability of this operating method in detecting water-logged goaf roadway’s shape,characteristics and scale,the author’s research group has conducted an case study in Shanxi’s coal mine.The research showed that the roadway-borehole TEM detection method is a great combination to underground geophysical exploration technology and drilling technology,and to make them supplement to each other.It is an effective application in goaf roadway with water detection.