基于深水区宽频地震的天然气水合物识别方法

仅利用地震似海底反射（BSR）识别琼东南盆地深水区天然气水合物存在一定的局限性，从而影响天然气水合物的勘探成效。笔者利用天然气水合物已钻井数据，分析该盆地深水区天然气水合物岩石弹性参数特征，用以查明天然气水合物的岩石物理规律；同时，利用地震正演模拟，明确了研究区发育的孔隙型、烟囱型水合物的地震反射特征。在此基础上，利用AVO正演判识真假BSR：天然气水合物底界面反射具有Ⅲ类AVO且存在AVO异常，此为真BSR反射；而块体流（MTD）底界面虽类似BSR反射，但其AVO为Ⅳ类且AVO无异常特征。利用宽频地震数据和三维地震速度体进行速度模型下的宽频确定性反演，并通过高速异常、高阻抗异常描述天然气水合物发育情况。总之，利用地震反射特征、AVO特征、无井宽频地震反演等手段，实现了琼东南盆地深水区多种类型天然气水合物的地震识别，判识圈定了水合物矿藏。

RESEARCH ON THE METHOD FOR GAS HYDRATE IDENTIFICATION BASED ON BROADBAND SEISMIC IN DEEP WATER AREAS

In the deep water areas of the Qiongdongnan Basin, it is difficult to make clear the occurrence of gas hydrate only with the seismic reflection data of BSR, which influences gas hydrate exploration. Based on the drilling data and the characteristics of the elastic parameters of gas hydrate bearing rocks in the basin, the physical properties of gas hydrate are clarified. Seismic forward modeling is adopted to distinguish the seismic reflection characteristics of the pore type hydrate from the chimney type hydrate. Then based on the AVO forward modeling, it is confirmed that the gas hydrate bottom interface (BSR) has the class Ⅲ AVO anomaly, while the MTD bottom interface, similar to the BSR reflection, shows the class Ⅳ AVO anomaly. Broadband seismic data and 3D seismic velocity volume are used for broadband deterministic inversion under the velocity model. With high velocity and high impedance anomalies, the occurrence and development status of gas hydrate are described. Integrating the methods of seismic reflection characteristics analysis, AVO characteristics analysis, well free broadband seismic inversion analysis and other means, various types of gas hydrate are discovered in the deep water area of the Qiongdongnan Basin, indicating the effectiveness of the broadband seismic method.