海洋辅助源宽频大地电磁方法

Marine auxiliary source broadband magnetotelluric method

受空气波影响,目前常用的海洋可控源电磁探测方法在浅水区几乎是探测盲区;由于海水的吸收衰减作用,大地电磁测深信号的高频成分在水域几乎衰减殆尽。因此,这两种方法在探测深度方面均存在不足之处。针对这一问题,提出海洋辅助源宽频大地电磁方法,将可控源音频大地电磁法应用于海洋资源勘探,开展混场源电磁数据采集,即在水面布设激发场源,在海底远区布设采集站接收电磁信号,可获得海洋可控源音频大地电磁信号。对这两组数据进行拼接处理,可实现海域宽频大地电磁探测。建立空气—海水—海底三层地电模型,计算水面激发—海底接收方式下的电磁场分量,分析了不同储层模型的宽频大地电磁视电阻率曲线特征,探讨了海洋可控源音频大地电磁分量的适应性及可行性。本项研究为海洋资源勘探与深部地球科学研究提供了有效的电磁探测方法。

Because of the influence of air waves,the shallow water area is almost a blind spot for the commonly used marine controlled source electromagnetic detection method.However,due to the absorption and attenua⁃tion of seawater,the high⁃frequency components of magnetotelluric sounding signals are seriously attenuated in water areas.Therefore,both methods have shortcomings in terms of depth detection.To solve this problem,this paper proposes the marine auxiliary source broadband magnetotelluric method,which applies the controlled source audio magnetotelluric method to marine resource exploration and carries out electromagnetic data acquisi⁃tion of mixed sources.In other words,the exciting source is deployed on the water surface in the far area,and the acquisition stations are deployed on the seabed to receive electromagnetic signals,so as to obtain the marine controlled source audio magnetotelluric data.By merging the two sets of data,broadband magnetotelluric detec⁃tion in the whole sea area is realized.In addition,a three⁃layer geoelectric model including air,seawater,and seabed is derived,and each component of the electromagnetic field for the surface-excitation and seafloorreceiving acquisition is calculated to simulate and analyze the adaptability and feasibility of the marine controlled source audio magnetotelluric components.By simulating the broadband apparent magnetotelluric resistivity curves of different models and analyzing their characteristics,a more suitable electromagnetic detection method is proposed for marine resource exploration and deep geoscience research.