Much of our knowledge of gas hydrate in the Dongsha area of the South China Sea has been gained through intensive geophysical surveys and drilling. However, many factors remain unclear, such as the co-existence of shallow gas hydrate and deeper gas hydrate. This lack of clarity is partially due to the lack of a depth-domain velocity model and accurate imagery of the gas hydrate-bearing sediments. In this study, pre-stack depth migration (PSDM) is used to produce subsurface images using a depth-domain velocity model from OBS tomography as the migration velocity. A simple initial velocity model was built using the seafloor depth information derived from multi-channel seismic (MCS) data. This simple model was used to build a more accurate velocity model by using first arrival time tomography from OBS data. Three different approaches were used to assess the reliability of the velocity model. Resolution tests and uncertainties analysis were used to further evaluate the model. The final PSDM image revealed some features more clearly than they were seen on the time migration image. These features help better explain the complex gas hydrate system. The depth of a bottom-simulating reflector (BSR) was picked directly from the PSDM image. This BSR is very consistent with the drilling result. Our work highlights the importance of PSDM in the study of gas hydrate in complex settings and highlights the potential and value of using OBS refraction in building shallow velocity models.

通过深入的地球物理调查和钻探，我们获得了南海东沙地区天然气水合物的许多知识。但是，许多因素仍不清楚，例如浅层天然气水合物和深层天然气水合物并存。这种缺乏清晰度的部分原因是由于缺乏深度域速度模型和含天然气水合物的沉积物的精确图像。在这项研究中，叠前深度偏移（PSDM）用于使用OBS层析成像的深度域速度模型作为偏移速度来生成地下图像。使用从多通道地震（MCS）数据获得的海底深度信息建立了一个简单的初始速度模型。通过使用OBS数据中的首次到达时间断层扫描，可以使用此简单模型来建立更准确的速度模型。三种不同的方法用于评估速度模型的可靠性。分辨率测试和不确定性分析用于进一步评估模型。最终的PSDM映像比在时间迁移映像上更清晰地揭示了某些功能。这些功能有助于更好地解释复杂的天然气水合物系统。直接从PSDM图像中提取底部模拟反射器（BSR）的深度。该BSR与钻探结果非常一致。我们的工作强调了PSDM在复杂环境下研究天然气水合物的重要性，并强调了在构建浅层速度模型中使用OBS折射的潜力和价值。最终的PSDM映像比在时间迁移映像上更清晰地揭示了某些功能。这些功能有助于更好地解释复杂的天然气水合物系统。直接从PSDM图像中提取底部模拟反射器（BSR）的深度。该BSR与钻探结果非常一致。我们的工作强调了PSDM在复杂环境下研究天然气水合物的重要性，并强调了在构建浅层速度模型中使用OBS折射的潜力和价值。最终的PSDM映像比在时间迁移映像上更清晰地揭示了某些功能。这些功能有助于更好地解释复杂的天然气水合物系统。直接从PSDM图像中提取底部模拟反射器（BSR）的深度。该BSR与钻探结果非常一致。我们的工作强调了PSDM在复杂环境下研究天然气水合物的重要性，并强调了在构建浅层速度模型中使用OBS折射的潜力和价值。