海底沉积物含天然气水合物后通常具有较高纵横波速度以及低密度特征,而常规叠后波阻抗反演只能获得波阻抗属性。由于水合物低密度特征导致含水合物地层波阻抗与周围地层存在叠置现象,因而,利用叠后波阻抗属性识别水合物储层存在一定误差。为了提高天然气水合物矿体的预测精度,提出采用叠前反演技术解决水合物储层预测精度低的问题。通过岩石物理分析明确天然气水合物储层敏感的弹性参数,在地震道集优化、精细合成记录标定以及初始模型建立的基础上,基于叠前反演技术对天然气水合物以及气态烃储层进行预测。研究结果表明:纵横波速度交会是研究区识别储层最敏感的弹性参数,并且基于坐标旋转技术重新构建的纵横波速度识别因子识别储层效果较好,能够清晰刻画水合物和气态烃储层;预测结果显示,研究区天然气水合物矿体呈近南北走向,在矿体的南部水合物和气态烃较为发育,与钻井情况吻合较好。该研究可为水合物储量计算提供可靠的面积和厚度依据。
Seabed sediments containing gas hydrate usually have high compressional and shear wave velocity and low density, while only wave impedance attributes can be acquired by conventional post-stack impedance inversion. Due to the low density of hydrates, the wave impedance of hydrate-bearing formation was superimposed with that of surrounding formation to a certain extent. Therefore, there was some error in identification of hydrate reservoirs by post-stack wave impedance. In order to improve the prediction accuracy of gas hydrate ore body, the pre-stack inversion technology was proposed to improve the low prediction accuracy of gas hydrate reservoirs. The sensitive elastic parameters of the gas hydrate reservoir were determined through the petrophysical analysis, and the gas hydrate and gaseous hydrocarbon reservoir were predicted with the pre-stack inversion technology on the basis of seismic trace set optimization, fine synthetic record calibration and initial model establishment. The results of the study show that The intersection of compressional and shear wave velocity was the most sensitive elastic parameter to identify the reservoir in the study area, and the identification factor of compressional and shear wave velocity was reconstructed based on the coordinate rotation technology and effective in identifying the reservoirs and characterizing the hydrate and gaseous hydrocarbon reservoirs clearly. The prediction results show that the natural gas hydrate ore body in the study area struck nearly from south to north, and the hydrate and gaseous hydrocarbon were relatively developed in the south of the ore body, which was in line with the drilling conditions. The prediction results can provide a reliable basis for hydrate reservoir calculation in terms of area and thickness.
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