摘要:
地—井瞬变电磁法是在地面发射、井(钻孔)中接收的装置形式,能够利用已有钻孔使接收探头深入地下更加接近目标体,获得更加可靠的信息.该装置对于深部低阻体,尤其当存在低阻覆盖层、矿化等地质干扰情况下,对于规模不大的深部良导矿体的探测能力较强.相对于磁性发射源,电性发射源勘查范围更广,适合地形起伏矿区开展工作.本文旨在通过研究电性发射源条件下钻孔中地下电性界面的异常特征,为实际勘查工作的定性分析提供参考.文中通过一维模型正演模拟对三分量瞬变响应异常特征进行了初步分析,结果表明,由于瞬变响应总场中叠加了背景场和异常场的响应,曲线形态复杂,仅在中晚期道电界面反映明显;而异常场曲线形态相对简单,对电性界面反映明显;整体上水平分量的异常显示度高于垂直分量.通过数值模拟分析获得了对于电性源地—井TEM钻孔中三分量曲线形态的初步认识,验证了电性发射源条件下地—井TEM对于确定电性界面的有效性,能够为进一步研究提供参考.
Abstract:
Borehole TEM is a configuration in which the transmitter is on the ground and the receiver probe is in borehole.The receiver can be installed near the orebody through the borehole and hence can obtain more reliable information of the orebody.Borehole TEM is effective for conductive mineralization,particularly in areas where the capability of surface EM for defining a target is limited either by large depths or by interfering conductive bodies such as overburden shallow sulfides and peripheral mineralized horizons.Relative to the magnetic source,the detection depth of electric source borehole TEM is deeper and it is more suitable for deep prospecting in the complex terrain area.Through the study of the borehole TEM response characteristics of electrical source of borehole TEM,the authors aim to provide technical support for the application.Three component response characteristics of half space,1D,3D model were analyzed through forward modeling,and its validity for different models was proved in this paper.The results show that,due to the superimposition of the background field and anomaly field response upon transient response of total field,the curve shape is complex,and the electrical interfaces are only obviously reflected at the middle and late stage.The shape of the anomalous field curve is relatively simple,and the electrical interface is obvious;the anomaly of the horizontal component is on the whole higher than that of the vertical component.In this paper,by means of numerical simulation analysis,the authors obtained the preliminary understanding of electrical source of downhole TEM three component curve shape and verified the effectiveness of the electrical interface under the condition of the electrical emission sources.The results obtained by the authors can provide a reference for the further research.
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