Numerical Modeling for Transient Anomalous Secondary Electromagnetic of Tabular Orebody in Borehole
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摘要: 通过研究井轴附近矿体瞬态场的响应特征, 为井中瞬变电磁场的勘探提供可靠的依据.应用时域有限差分法和Mur吸收边界, 对磁偶源产生的瞬变电磁场进行三维数值模拟, 建立了全空间内不同埋深、不同大小、不同倾角的低阻矿体和高阻矿体的地电模型.在数据处理过程中, 排除导电全空间对二次场的影响, 得到反映目标体异常情况的异常二次场.通过分析不同导电模型瞬变场的特征规律, 结果表明: 不同埋深、大小、倾角和电导率的矿体具有不同的响应特征, 且差异较大.该方法对识别井中板状矿体有较为明显的作用.Abstract: The transient electromagnetic response of conductive orebody is studied so as to provide a reliable basis for the exploration of the transient electromagnetic in borehole. Finite-different time-domain method and Mur absorbing boundary were used to simulate three-dimensional transient electromagnetic field generated by magnetic dipole source, and establishing the geometric model of low resistivity orebody with different depth, different sizes, different dips, as well as high resistivity orebody in the whole space. During the data processing, excluding the impact of conductive whole space to the total response and getting the anomalous secondary field which reflects the target characteristics. The regularity of the geometric model was analyzed, and the result shows that the orebody with different depth, sizes, dips and conductivity have very different response. The method for identification of tabular orbody has a significant effect.
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图 1 均匀全空间发射和接收线圈组合方式剖面
Fig. 1. The transmitting and receiving coil in homogeneous medium
图 2 井中均匀全空间点(5, 0, 50) 处解析解与数值解
a.电场解析解与数值解对比曲线; b.数值解相对误差曲线
Fig. 2. The analytical and numerical solution in the point (5, 0, 50) of homogeneous medium
图 3 井中全空间二次电场剖面曲线
a.均质全空间; b.含低阻倾斜矿体的全空间; c.t =0.896 μs均质全空间与含低阻倾斜矿体的全空间对比
Fig. 3. Secondary electric field borehole profiles in homogeneous medium
图 4 井中低阻水平矿体的异常二次电场剖面曲线
a.钻孔穿过矿体; b.钻孔未穿过矿体; c.钻孔未穿过矿体且薄板临近发射线圈
Fig. 4. The anomalous secondary electric field borehole profiles of low resistivity horizontal orebody
图 5 井中不同尺寸低阻水平矿体的异常二次电场剖面曲线
a.8 m×8 m×2 m; b.16 m×16 m×2 m; c.24 m×24 m×2 m
Fig. 5. The anomalous secondary electric field borehole profiles of low resistivity horizontal orebody in different sizes
图 6 矿体Y轴方向边长b和X轴方向边长a与异常二次电场之间的关系
Fig. 6. The relationship between the anomalous secondary field and orebody side-length (a and b)
图 7 钻孔穿过低阻倾斜矿体的异常二次电场剖面曲线
a.α =30°; b.α =45°; c.α =60°
Fig. 7. The anomalous secondary electric field borehole profiles of low resistivity inclined orebody drilled
图 8 钻孔未穿过低阻倾斜矿体的异常二次电场剖面曲线
a.α =30°; b.α =45°; c.α =60
Fig. 8. The anomalous secondary electric field borehole profiles of low resistivity inclined orebody not drilled
图 9 水平高阻矿体异常二次磁场垂直分量剖面曲线
a.t =0.77 μs均质全空间与含高阻矿体的全空间对比; b.钻孔穿过矿体; c.钻孔未穿过矿体
Fig. 9. The anomalous secondary z-magnetic field borehole profiles of high resistivity horizontal orebody
图 10 井中不同尺寸高阻水平矿体的异常二次磁场垂直分量剖面曲线
a.8 m×8 m×2 m; b.16 m×16 m×2 m; c.24 m×24 m×2 m
Fig. 10. The anomalous secondary z-magnetic field borehole profiles of high resistivity horizontal orebody in different sizes
图 11 钻孔穿过高阻倾斜矿体的异常二次磁场垂直分量剖面曲线
a.α =30°; b.α =45°; c.α =60°
Fig. 11. The anomalous secondary z-magnetic field borehole profiles of high resistivity inclined orebody drilled
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