Abstract The deep-towed Autonomous Cable Seismic (ACS) system is a high-resolution acoustic survey system designed for use in deep-water environments. This system uses a high-frequency acoustic source and a multichannel receiver cable. A common problem in the analysis of deep-towed ACS data is the unstable positioning of the source and receivers due to ocean currents and seafloor bathymetry. Since the data acquisition using high-frequency source with unstable source–receiver positions causes destructive interference on the final stack profile, correction of the unstable source-receiver is a crucial issue. In this study, we propose a method to solve the unstable source–receiver position problem and thus to construct an accurate final stack profile. We used deep-towed ACS data acquired in the Joetsu Basin in Niigata, Japan, where hydrocarbon features in the form of gas chimneys, gas hydrate, and free gas have been observed. Because sidelobes in the ACS source signature defocus the source wavelet and decrease the bandwidth frequency content, we designed a filter to focus the source signature. Our proposed approach considerably improved the quality of the final stack profile. Even though depth information was not available for all receivers, the velocity spectra in the velocity analysis were well focused. Furthermore, shaping the source wavelet considerably increased the bandwidth frequency of the source signature. We applied seismic attribute analysis to the post-stack profile to identify the distributions of free gas and hydrate. Our seismic attribute analyses for the high-frequency ACS data demonstrated that free gas accumulations are characterized by low reflection amplitude and an unstable frequency component, and that hydrate close to the seafloor can be identified by its high reflection amplitude.

中文翻译：

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天然气水合物勘探深拖高频地震系统资料处理与解释方案

摘要 深拖自主电缆地震（ACS）系统是一种高分辨率声学勘测系统，设计用于深水环境。该系统使用高频声源和多通道接收器电缆。深拖 ACS 数据分析中的一个常见问题是由于洋流和海底测深导致的源和接收器定位不稳定。由于使用具有不稳定源 - 接收器位置的高频源进行数据采集会对最终的堆叠剖面造成破坏性干扰，所以不稳定的源 - 接收器的校正是一个关键问题。在这项研究中，我们提出了一种解决不稳定源 - 接收器位置问题的方法，从而构建准确的最终堆栈剖面。我们使用了在日本新泻的上越盆地获得的深拖 ACS 数据，其中已观察到气烟囱、天然气水合物和游离气等形式的碳氢化合物特征。由于 ACS 源特征中的旁瓣使源小波散焦并降低了带宽频率内容，因此我们设计了一个滤波器来聚焦源特征。我们提出的方法大大提高了最终堆栈配置文件的质量。尽管并非所有接收器都可以获得深度信息，但速度分析中的速度谱得到了很好的聚焦。此外，对源小波进行整形大大增加了源签名的带宽频率。我们将地震属性分析应用于叠后剖面，以确定游离气体和水合物的分布。