南海北部荔湾3区块天然气水合物分布特征及目标识别

针对天然气水合物钻探与取样难以解决的水合物矿体空间展布等问题,利用白云-荔湾凹陷高密度分析重新处理的三维地震资料,首先基于模糊数学的多属性融合技术对水合物分布进行刻画;再通过高分辨率速度场对浅层开展高分辨率宽频无井反演技术,提高了水合物层分辨率;最后,利用岩石物理方法及多种模型对水合物饱和度进行定量预测,实现了对5～6m厚水合物层的有效辨别,进而形成了一套适合于孔隙充填型的水合物矿藏目标识别评方法。结果表明:应用该技术可有效对荔湾3水合物富集区第四条带水合物空间刻画,揭示出该区水合物饱和度最高可超40%,同时薄层与厚层水合物具有明显互层分布特征,在水合物矿体刻画及饱和度预测基础上,进一步对该区实施了井位优选,该方法预测的水合物层与实际钻探H1和H2站位吻合较好。这些结果说明常规三维油气地震数据在经过宽频处理后可应用于高分辨率水合物勘探,节约经济成本,同时提高了常规地震在水合物勘探中精度与实用性。

The distribution and characteristics of gas hydrate in the Liwan3, northern slope of the South China Sea

Many gas hydrate drilling sites and core samples have indicated that there are various types of natural gas hydrates in the northern slope of the South China Sea. However, the drilling data only shows the distribution of gas hydrate near the borehole location. It is still difficult to know how about the spatial distribution of gas hydrate away the drilled sites. High density analysis was used to reprocess the conventional three dimensional seismic volumes in the Baiyun-Liwan sag. Multi-attribute analysis based on fuzzy mathematics was used to predict the gas hydrate distribution. Then, high-resolution broadband inversion without the well limitation was conducted based on the high-resolution velocity analysis, which increased the resolution of identifying gas hydrate-bearing layers. Finally, several rock physical models were involved to quantitatively predict gas hydrate saturation using the inverted P-wave velocity, which has been used to describe the gas hydrate-bearing layers with a thickness ranging from 5 to 6 m. The method for pore-filling gas hydrate was proposed to identify and evaluate gas hydrate layer in this study. The distribution of gas hydrate at fourth hydrate zone in the Liwan 3 was proved to contain gas hydrate. The maximum value of gas hydrate saturation is over 40%, and that the thin gas hydrate layer is interbedded with thick layer. The actual drilling results at Sites H1 and H2 are in good accordance with the pre-drilling predictions, which has already proved the applicability of our proposed approach.