海洋可控源电磁法对天然气水合物高阻薄层的可探测度

为了便于分析海洋可控源电磁法(CSEM)对天然气水合物高阻薄层的探测能力,定义了一个反映目标层可探测程度的量——可探测度,目标层可探测度越大,表明越容易被探测到。计算了不同水深情况下一维水合物模型的海洋CSEM归一化场、有效异常和可探测度。结果表明,在深水环境下,利用归一化场、有效异常和可探测度均可以识别水合物高阻薄层,但在浅水环境下,归一化场和有效异常受空气波畸变影响严重,不能很好地识别高阻薄层,而空气波对可探测度影响较小,在浅水区利用可探测度有利于识别水合物高阻薄层。

DETECTIVITY OF HIGH-RESISTIVITY GAS HYDRATE LAYERS WITH MARINE CSEM METHOD

In this paper, we investigated the resolution of marine Controlled-Source Electro-Magnetic (CSEM) data for thin high resistivity gas hydrate layer. We introduced the term of detectivity that incorporates both the amplitude and phase information in this discussion. The analyses of the 1D CSEM data show that in deep water environment, the three diagnostic tools (the normalized amplitude ratio, the effective anomaly and the detectivity) can give a reliable diagnostic signature of gas hydrate. In shallow water, however, both the normalized field and the effective anomaly are poor diagnostic tools, heavily affected by air waves. The detectivity is hardly affected by air waves. For all water depths, it is a good diagnostic tool for a thin reservoir of high resistivity.