海洋油气勘探中电磁法频率域2.5维正演研究

以南海某海盆为背景,根据地震资料圈定靶区,用2.5维频率域正演程序进行数值模拟,用距海底150 m的水平电偶极子源激发0.01~1 Hz的低频电磁波,海底沉积层的异常区域填充海水、油和气等不同电阻率介质,采用沉底式观测装置观察其沿偶极方向的电场响应。结果表明,海洋2.5维频率域电磁法可以较为清晰地区分海底油气和水等高阻异常,将不同发射频率的电场响应等值线图叠放在一起,可以确定在一定电阻率假设下,分辨率最好的发射频率。与三维电磁法和一维电磁法相比较,2.5维正演在有效性和效率方面都有较大的优势,可为以后实际海洋油气勘探工程实践提供技术指导和设计参考。

On2.5D frequency domain forward modeling of CSEM in exploration of offshore oil and gas

Series of 2.5D frequency domain numerical simulations have been played, taking some sea basin in South China Sea for background and delineating target district according to earthquake information. Low frequency electromagnetic waves of 0.01-1Hz are activated by a horizontal electric dipole which is 150m from sea floor, while exception region in deposition layer is filled with such different resistance rate media as seawater, oil and gas. Then, sink type observation device is used to observe electric field response along the same direction as the electric dipole. Results showed that 2.5-dimensional frequency domain CSEM is helpful to clearly distinct the high resistance anomaly of subsea oil, gas and water, more than that, the frequency point of best resolution is found assuming side-bed resistivity, when electric field contour stacking together. Compared with the three-dimensional and one-dimensional forward electromagnetic method, two-dimensional forward method has a great advantage in terms of effectiveness and efficiency, also can provide technical guidance and design reference for practical engineering of offshore oil and gas exploration.