煤矿富水体SOTEM响应三维数值模拟研究

Three-dimensional numerical simulation of short-offset transient electromagnetic responsesto water-rich bodies in coal mines

采用三维时域有限差分法对三维地电模型的SOTEM响应进行正演计算,发现:(1)采空区或陷落柱上方观测的电场E_x响应衰减曲线在早期高于背景响应,在晚期均低于背景响应;(2)偏移距越小,∂B_(z)/∂t响应信号的相对异常越大,发射源长度的增加能提升信号强度,但同时也会导致相对异常的略微下降;(3)当测线靠近发射源时,采空区或含水陷落柱的∂B_(z)/∂t响应在整体上低于背景值,当测线远离发射源时,采空区或含水陷落柱的∂B_(z)/∂t响应在整体上高于背景值。本文计算结果对于认识SOTEM对煤矿典型富水体的探测能力具有重要意义,为SOTEM装置参数选取及其在煤炭领域的推广应用打下理论基础。

This study performed forward modeling for the short-offset transient electromagnetic(SOTEM)responses of a three-dimensional geoelectric model using the three-dimensional finite-difference time-domain method.The results reveal that:(1)The attenuation curves of the E x responses from the electric field above the goaf or collapse column were above the background response curve at early times but below it at later times;(2)A shorter offset corresponded to a higher relative anomaly of∂B_(z)/∂t response signals.Increasing the length of the transmitting source could enhance the signal intensity while slightly decreasing the relative anomaly;(3)In the case of survey lines close to the transmitting source,the overall∂B_(z)/∂t responses of the goaf or collapse column were weaker than the background responses.For survey lines away from the transmitting source,the overall∂B_(z)/∂t responses of the goaf or collapse column were stronger than the background responses.In summary,the calculation results demonstrate significant implications for understanding the ability of the SOTEM method to detect typical water-rich bodies in coal mines,laying a theoretical foundation for the parameter selection of SOTEM devices and their generalized application in the coal sector.