浅埋煤层采空积水区TEM与CSAMT探测优化反演

Optimized inversion of TEM and CSAMT detection in goaf water accumulation area of shallow coal seam

综合物探是圈定浅埋煤层采空积水区的有效方法,常规的中心回线瞬变电磁法(TEM)在反演非中心点数据时,存在计算误差。可控源音频大地电磁法(CSAMT)探测频率范围跨度大,对浅部地质体的分辨能力差。采用大定源TEM一维正演,计算了偏离发射回线中心不同位置测点的瞬变电磁响应,与中心点相比,偏离距越大,早期信号畸变越严重,以大定源TEM一维正演理论为基础,反演计算了非中心点数据,计算结果准确还原了模型的电性特征;对CSAMT频率进行优化,结合目标层埋深,加密对应埋深范围内的频点,提高CSAMT对浅埋地质体的分辨能力。通过正演模拟和实测数据处理,结果表明:大定源TEM一维反演可以消除偏离距带来的早期信号偏差,还原模型的真实电阻率响应;优化频率的CSAMT采集更丰富的浅部地层信息,实现对浅埋地质体的探测,2种方法综合探测,结果相互验证,消除了单一方法的多解性,探测结果更加可靠,是一种针对浅埋煤层采空积水区精确探查的有效方法,经钻探验证,结果准确。

Comprehensive geophysical prospecting is an effective method to delineate the water accumulation area in the gobin shallow coal seams.The conventional TEM method has calculation error when inverting non-central point data.The controllable source audio magnetotelluric method(CSAMT)has a wide detection frequency range and poor resolution to shallow geological bodies.In this paper,one-dimensional forward modeling of large fixed-loop TEM is used to calculate the transient electromagnetic response of different measuring points at different positions offset from the center of the transmission loop.Compared with the center point,the larger the deviation distance,the more serious the early signal distortion.Based on the one-dimensional forward modeling theory of large fixed-loop TEM,the non-center point data is calculated inversely,and the calculation results accurately restore the electrical characteristics of the model.The CSAMT frequency is optimized and combined with the buried depth of the target layer,the frequency points within the corresponding buried depth range are encrypted to improve CSAMT’s ability to distinguish shallow buried geological bodies.Through forward simulation and measured data processing,the results show that large fixed-loop TEM one-dimensional inversion can eliminate the early signal deviation caused by offset distance and restore the true resistivity response of the model.CSAMT with optimized frequency points can collect abundant information to realize the detection of shallow buried geological bodies.The results of this two optimal methods are verified by each other,which eliminates the multiple solutions of a single method and makes the detection results more reliable.It is an effective method for the accurate exploration of the gob water area in the shallow buried coal seam,and the results are accurate.