华北煤田瞬变电磁勘探深度研究

Study on the exploration depth of transient electromagnetic method in northern China coalfield

为研究瞬变电磁勘探在华北煤田的勘探深度,利用瞬变电磁感应电压晚期段表达式,通过指定仪器最小可分辨电压,推导出瞬变电磁勘探最晚可检测出有效信号时间及最大探测深度表达式,计算了特定情况下的极限探测深度和最晚有效信号检出时间:在发射磁矩为10002×20 A.m2,地层电阻率分别为10和100Ω.m时,瞬变电磁勘探最晚有效信号检出时间为209.6 ms和52.6 ms,最大探测深度为1823 m和2889 m;以实测典型华北煤系地层瞬变电磁曲线为例,其计算机反演深度达1400 m;结果表明:采用合适的仪器和正确的工作装置,瞬变电磁勘探可以满足华北煤田目前开采深度的勘探需要.

For the study on the exploration depth of transient electromagnetic method （TEM） in northern china coalfield, the formulas to calculate the time of latest detectable signal and the maximum depth of exploration were developed from the formula for late time apparent resistivity by assuming the minimum detectable signal of instrument, also the time of the latest detectable signal and the maximum exploration depth for some conditions were calculated： when the transmit moment is 1000^2 × 20 A·m^2 ,and the resistivity of the earth is 10 and 100 Ω·m respectively, the time of latest detectable signal is 209.6 ms and 52.6 ms, the maximum depth of exploration is 1823m and 2889m. A typical TEM exploration curve acquired in a coalfield in northern China was inversed using 1-D inversion software and the maximum depth is 1400 m. The results show that TEM can satisfy the depth demanded to the exploration in northern China coalfield if appropriate instrument is applied and the correct array is adapted.