西沙海域天然气水合物的地震响应特征及分布

Seismic response and distribution of gas hydrates in the sediments of Xisha waters

海洋天然气水合物在地球物理资料上具有典型的似海底反射（BSR）特征，同时表现有振幅空白反射、低地震频率、高波阻抗及三类AVO响应等地球物理特征.根据最近油气勘探地震资料分析，在西沙海域沉积层中发现典型的BSRs，BSR一般分布在海底以下300~400 m，与地层斜交，还在BSR之上发现振幅空白，空白反射的时间厚度大约为50~100 ms.在叠前地震道集上，BSR下伏的游离气层具有三类AVO响应特征.综合地震振幅、频率、波阻抗、叠前道集响应等地球物理特征，推断西沙海域存在广泛分布的天然气水合物.

Marine gas hydrates are usually characterized by typical bottom seafloor reflection （BSR）, blank zone, and low seismic, frequency, high P-impedance and type III AVO. According to the analyses of new seismic data, we indentified typical BSRs in the sediments of the Xisha waters. BSRs occurred 300~400 m below seafloor and crossed the sedimentary layers. The blank zone occurred above BSR with thickness of 50~100 ms. In the prestack, Free gas below BSRs has type III AVO. All geophysical evidence suggested that the gas hydrates were widely distributed in Xisha waters.