(1. 中南大学 有色金属成矿预测教育部重点实验室，长沙 410083；
2. 中南大学 地球科学与信息物理学院，长沙 410083；3. 北京矿产地质研究院，北京 100012；
4. 中国石油长庆油田分公司 勘探开发研究院，西安 710018；
5. 低渗透油气田勘探开发国家工程实验室，西安 710018)
摘 要: 采用伪随机信号源的广域电磁法具有探测深度大、精度高、抗干扰能力强、效率高等优点，正成为新的研究热点。E-Ex广域电磁法已经实现了一维和二维正反演。但地球介质是复杂的三维结构，所采集到的数据需要进行三维反演和解释，为了进一步提高广域电磁法的数据处理和解释精度，迫切需要进行广域电磁法三维正反演研究。采用积分方程法实现E-Ex广域电磁法三维正演，首先对均匀半空间中存在低阻异常体进行了数值模拟，发现广域视电阻率不仅具有比CAGNIARD视电阻率更优的分辨能力，且广域视电阻率的场源阴影效应相对CAGNIARD视电阻率有所减弱；然后对均匀半空间中存在高阻异常体进行了数值模拟，结果表明CAGNIARD视电阻率对高阻体响应不明显，而广域视电阻率有良好反映。研究表明，无论是高阻还是低阻异常体，广域视电阻率的分辨能力都优于CAGNIARD视电阻率。
关键字: 广域电磁法；广域视电阻率；积分方程法；数值模拟
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China;
3. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;
4. Research Institute of Exploration and Development, PetroChina Changqing Oilfield Company,
Xi’an, 710018, China;
5. National Engineering Laboratory for Exploration & Development of Low-Permeability Oil＆Gas Fields,
Xi’an 710018, China）
Abstract:In the study of E-Ex wide field electromagnetic method, one-dimensional (1-D) forward modeling and inversion has been achieved, there are only a few number of publications related to the three-dimensional (3-D) forward modeling and inversion study. In the field work, the geological situation is complex, and the data needs 3-D inversion and interpretation, so 3-D forward modeling, inverse and interpretation become the bottleneck of wide field electromagnetic method. There is an urgent need for 3-D modeling of wide field electromagnetic method. Integral equation method was applied to achieve E-Ex wide field electromagnetic method 3-D modeling. Firstly a single low resistivity anomalous target body within homogeneous half-space was simulated, and it was found that not only the wide field apparent resistivity has better resolution capability than CAGNIARD apparent resistivity, but also the effect of the source and non-plane wave effect was weakened for wide field apparent resistivity. Then, a single high resistivity anomalous target body within homogeneous half-space was simulated, and it was found that, for the high resistivity body response, the CAGNIARD apparent resistivity is hard to distinct, but the wide field apparent resistivity has great resolution capability. The analysis shows that no matter the anomalous has high resistivity or low resistivity, the resolution of wide field apparent resistivity is better than that of the CAGNIARD apparent resistivity.
Key words: wide field electromagnetic method; wide field apparent resistivity; integral equation method; numerical simulation
