程久龙,姜成麟,李垚,等. 钻孔瞬变电磁法方位线圈扫描探测定位方法[J]. 煤炭学报,2024,49(1):616−627. DOI: 10.13225/j.cnki.jccs.YH23.1225
引用本文: 程久龙,姜成麟,李垚,等. 钻孔瞬变电磁法方位线圈扫描探测定位方法[J]. 煤炭学报,2024,49(1):616−627. DOI: 10.13225/j.cnki.jccs.YH23.1225
CHENG Jiulong,JIANG Chenglin,LI Yao,et al. Research on borehole transient electromagnetic positioning method of azimuthal coil scanning detection[J]. Journal of China Coal Society,2024,49(1):616−627. DOI: 10.13225/j.cnki.jccs.YH23.1225
Citation: CHENG Jiulong,JIANG Chenglin,LI Yao,et al. Research on borehole transient electromagnetic positioning method of azimuthal coil scanning detection[J]. Journal of China Coal Society,2024,49(1):616−627. DOI: 10.13225/j.cnki.jccs.YH23.1225

钻孔瞬变电磁法方位线圈扫描探测定位方法

Research on borehole transient electromagnetic positioning method of azimuthal coil scanning detection

  • 摘要: 利用掘进巷道超前探水钻孔进行钻孔瞬变电磁法探测钻孔孔壁外围远距离含水体,避免了常规测井方法仅能探测钻孔孔壁岩层的“一孔之见”。目前钻孔瞬变电磁法受全空间效应的影响,接收到的单分量响应不能判别异常体方位;多分量响应可以近似判断异常体的大致方位,但难以通过成像等直观有效的方法对其进行精确定位。基于钻孔瞬变电磁法和方位电磁波测井相关理论,提出了钻孔瞬变电磁法方位线圈扫描探测定位方法,采用方位线圈作为探测装置,减小线圈互感,增强钻孔瞬变电磁法的探测效果。同时,通过改变线圈旋转角,对钻孔孔壁进行360°扫描,形成钻孔径向全方位探测,旨在对钻孔孔壁外围岩体中的低阻体进行精确定位。首先推导方位线圈的互感解析表达式,探讨方位角对方位线圈互感的影响,通过数值计算确定最佳方位角取值。分别建立均匀介质和含低阻异常体的钻孔全空间三维地质−地球物理模型进行瞬变电磁场数值模拟,分析方位线圈的瞬变电磁法扫描探测多分量响应特征,总结方位线圈扫描探测瞬变电磁响应规律,确定了钻孔瞬变电磁法方位线圈扫描探测定位方法,即通过钻孔轴向和径向的瞬变电磁响应特征判别钻孔孔壁外围岩体中低阻异常体的位置。最后建立含2个低阻体的地质−地球物理模型,采用最佳方位角的方位线圈进行数值实验,验证了该方法能有效地判别低阻异常体的方位。研究表明:钻孔瞬变电磁法方位线圈扫描探测结果可以较好地反映钻孔径向外围岩体中低阻异常体引起的瞬变电磁场异常,全空间视电阻率成像结果分辨率较高。依据钻孔轴向和径向的瞬变电磁响应特征,钻孔瞬变电磁法方位线圈扫描探测定位方法对钻孔孔壁外围岩体中的低阻异常体具有较高的分辨率及定位精度。研究结果可以为钻孔瞬变电磁法方位线圈扫描探测定位方法的实际应用提供理论依据。

     

    Abstract: The borehole transient electromagnetic method is used to detect the long-range water-bearing bodies around the borehole wall by using the advanced water exploration borehole in the heading roadway, which avoids the “one’s opinion in one hole” because the normal logging methods can only detect the rock layer of the borehole wall. At present, because of the whole space effect, the current borehole transient electromagnetic method cannot distinguish the orientation of abnormal bodies by the received single-component response, and it can approximate the orientation of abnormal bodies by multi-component response, but it is difficult to precisely locate and interpret the profiles by the visual and effective means such as imaging. Based on the theory of borehole transient electromagnetic method and azimuthal electromagnetic logging, this paper proposes a borehole transient electromagnetic positioning method with azimuthal coil scanning detection. The azimuth coil is used as the detection device to reduce the mutual inductance of the coil and enhance the detection effect of the borehole transient electromagnetic method. At the same time, by changing the rotation angle of the coil, the borehole wall is scanned by 360° to form a radial all-round detection of the borehole, aiming at a precise localization and profile interpretation of low-resistance abnormal bodies in the rock mass at the periphery of the borehole wall. Firstly, the authors derive an analytical expression for the mutual inductance of an azimuth coil, discuss the effect of azimuth angle on azimuth coil mutual inductance, and determine the optimum azimuth angle by numerical calculation. Secondly, a full-space 3D geological-geophysical model of the borehole with homogeneous medium and low-resistance abnormal bodies are established respectively and the numerical simulation of transient electromagnetic field is carried out. The multi-component response characteristics of the azimuthal coil scanning detection transient electromagnetic response are analyzed, and the law of transient electromagnetic response of azimuthal coil scanning detection is summarized, and the borehole transient electromagnetic positioning method with azimuthal coil scanning detection is determined. Namely, through the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the position of the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall is determined. Finally, by establishing the geological-geophysical model with two low-resistance bodies and using azimuth coils set to the best azimuth angle for numerical experiments, it is verified that the method can intuitively and effectively determine the orientation of low resistance abnormal bodies. The study shows that the azimuth coil scanning detection results of the borehole transient electromagnetic method can better reflect the transient electromagnetic field anomaly caused by the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall, and the resolution of the full-space apparent resistivity imaging results is high. Based on the transient electromagnetic response characteristics of the axial and radial directions of the borehole, the borehole transient electromagnetic positioning method with azimuthal coil scanning detection has a high resolution and localization accuracy for the low-resistance abnormal bodies in the rock body at the periphery of the borehole wall. The research results provide a theoretical basis for the practical application of the borehole transient electromagnetic positioning method with azimuthal coil scanning detection.

     

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