浅水区的瞬变电磁法:一维数值模拟结果分析(英文)

TRANSIENT ELECTROMAGNETIC IN SHALLOW WATER:INSIGHTS FROM 1D MODELING

在浅水环境中,利用频率域海洋可控源电磁法探测油气藏薄层面临着挑战,这是因为空气波支配着电磁响应而它只含有少量海底电阻率结构的信息.本文研究了空气波对时间域可控源电磁(CSEM)响应的影响.空气波到达时间取决于海水深度.在浅水区空气波到达早,而在深海水区空气波到达晚,空气波与来自深部电阻体的电磁波出现在不同时间段.虽然在中等深度的海水区空气波和来自深部电阻体的电磁信号几乎同时到达,但与不含有油气藏的背景模型相比,仍可以看到明显的异常.浅水区勘探的好处在于可以使用表面拖曳系统.

In shallow water environments, the frequency domain, marine controlled source electromagnetic （CSEM） method faces a challenge for detecting thin hydrocarbon reservoirs because the airwave dominates electromagnetic responses and contains little information about resistivity structure of the seabed. In this paper, airwave effects on time domain （or transient） CSEM responses are investigated. The arrival time of the airwave depends on the water depth. The airwave arrives earlier in shallow water and later in deep water environments and it occurs at different time than the signals traveling through the deep resistor. Although in an intermediate water depth the airwave and the signal from the deep resistivity arrive at about the same time, one can still see a clear anomaly compared to the background model without hydrocarbon reservoirs. For shallow water surveys, one has the added advantage that a surface towed system can be used.