南海北部陆坡神狐海域含水合物沉积层时频特征提取及识别方法

Time-frequency signature extraction and recognition of unconsolidated sediments containing gas hydrate and free gas in Shenhu area , Northern South China Sea

南海北部陆坡神狐海域是天然气水合物发育的有利区域,天然气水合物在时间-频率域具有独特的响应特征.结合研究区最新处理的高分辨率三维地震资料、测井和钻井解释成果,采用基于连续小波变换的时频分析方法,可以实现对含水合物沉积层及其下伏游离气沉积层在时间-频率域成像.通过分析,在研究区识别出低频低能、高频低能、低频高能、高频高能、低频盲区和高频盲区等多种频率异常,发现频率异常与游离气饱和度、水合物饱和度、裂隙发育情况及调谐效应密切有关,认为水合物存在带可以通过寻找低频高能、高频低能或高频盲区之上的低频低能、高频高能或高频低能区识别.研究证明基于时频分析的时间-频率域水合物识别方法其分辨率明显高于时间-振幅方法,即使是在时域剖面BSR特征不明显时,也可以对含水合物层进行识别,因此,获取的时频特征也可以作为水合物识别的直接指示.

The gas hydrate petroleum system in Shenhu Area of northern South China Sea is considered to be one of the promising targets for exploration and exploitation. Combining time-frequency information from seismic reflection data sets allows the analysis of anomalous reflections from very-shallow to great subsurface depths. Time-frequency analysis method enhances the imaging of subsurface features which have a frequency-dependent reflectivity such as hydrate and gas. The interpretation method has been used to our study area~ The seismic imagery shows several anomalous reflection amplitudes, such as low frequency low intensity anomalies, low frequency high intensity anomalies, high frequency low intensity anomalies, high frequency high intensity anomalies, low frequency blackout anomalies and high frequency blackout anomalies. Research result shows that low frequency low intensity anomalies and high frequency low intensity or high frequency high intensity anomalies overlvin~ low fr^rl,,~ I^l~ ; ：...and high frequency low intensity or high frequency blackout anomalies may be attributed to the occurrence of gas hydrate. We conclude that this technique has a good potential to assist seismic study of structures associated with gas hydrates accumulations.