| 陆地可控源电磁法探测效果的频率响应 |
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| 引用本文： | 万伟,唐新功,黄清华.陆地可控源电磁法探测效果的频率响应[J].地球物理学报,2019,62(12):4846-4859. |
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| 作者姓名： | 万伟 唐新功 黄清华 |
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| 作者单位： | 北京大学地球与空间科学学院地球物理学系,北京,100871;2“油气资源与勘探技术”教育部重点实验室(长江大学),武汉430100;长江大学非常规油气湖北省协同创新中心,武汉430100 |
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| 基金项目： | 国家自然科学基金（41574104，41674107）资助. |
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| 摘 要： | 陆地可控源电磁法的观测资料可依据频段范围近似地划分为近区场、中间区场及远区场,但采用测量相互正交电、磁分量,并计算视电阻率的资料处理方式只适用于远区场数据.为更有效地利用陆地可控源电磁法不同区间场的观测资料,本文结合三维数值模拟技术并采用电场分量直接进行反演的策略,对不同区间电场的响应特征与探测效果进行了分析.数值模拟结果表明:近区电场的异常响应最明显,异常响应不随频率发生显著变化,但纵向分辨能力差;远区电场异常响应随频率发生显著变化,其探测深度取决于频率的高低;中间区场较为复杂,地表电场异常响应的等值线中心并不是位于异常体中心正上方,而是在沿场传播方向上向异常体与围岩的分界面处偏移,并且发现中间区场资料的加入会影响反演结果的准确性.综合合成数据和野外实测资料的反演结果,发现结合近区场和远区场资料而舍弃中间区场资料的反演效果更佳,这为陆地可控源电磁法资料的反演解释提供了一种有效途径.
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| 关 键 词： | 陆地可控源电磁法 场区 频率组合 三维正反演 |
| 收稿时间： | 2019-02-26 |
Frequency effect on land CSEM sounding |
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| WAN Wei,TANG XinGong,HUANG QingHua.Frequency effect on land CSEM sounding[J].Chinese Journal of Geophysics,2019,62(12):4846-4859. |
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| Authors: | WAN Wei TANG XinGong HUANG QingHua |
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| Institution: | 1. Department of Geophysics, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Key Laboratory of Exploration Technologies for Oil and Gas Resources of MOE, Yangtze University, Wuhan 430100, China;3. Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan 430100, China |
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| Abstract: | The land controlled-source electromagnetic (CSEM) method observes the electromagnetic field of wide frequency band excited by single source. According to the physical nature of the electromagnetic field in frequency domain, the observation of the land CSEM method can be approximately divided into three sections:the near-zone field, the middle-zone field and the far-zone field. The conventional land CSEM method such as CSAMT only uses the far-zone field data, which possibly fails to utilize the information contained in the near-zone and middle-zone. We have developed 3D forward and inversion tool for land CSEM method, which is based on the open source EM modular platform ModEM. Our algorithm solves the primary and secondary electrical field separately in the forward modeling, and directly fits Ex component in all of the three zones in the inversion scheme. After discussing the response of electric field Ex in different field zones, we investigate the best frequency combinations for 3D inversion. The 3D CSEM numerical simulation shows that in near-zone field the abnormal response of Ex has large amplitude and does not change with frequency significantly, and the inversion result of the synthetic data shows that the near-zone field has poor resolution in depth. The simulation also shows that the center of the surface Ex abnormal response contour in the middle-zone field is not located above the center of the anomaly body, but is offset from the transverse electrical interface of resistivity model, which results in the deviation of the inverted resistivity anomaly from the actual position in the synthetic inversion test. The far-zone field Ex abnormal response varies with frequency, which can be used to distinguish the electrical layers at different depths. By comparing and analyzing the inversion results of different frequency combinations of synthetic data and field data, we find that for land CSEM 3D inversion the best frequency choice is to combine the data in the near-zone field and far-zone field together, abandon the data in middle-zone field. |
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| Keywords: | Land CSEM Field-zone Frequency combination 3D forward and inversion |
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