The application of post-stack impedance inversion without well to the prediction of gas hydrate distribution in T study area

Aimed at investigating the geological conditions and the modes of occurrence of gas hydrate on the northern slope of South China Sea, the authors established a three?dimensional interval velocity model based on the three?dimensional seismic data and stacking velocity spectrum under the condition of lack of logging data, and then transformed the data to low impedance background model. Sub?sequently, the authors extracted pseudo wells and tied them accurately, and finally obtained an absolute impedance and fine velocity bodies by the constrained sparse spike inversion method. Meanwhile, the authors comprehensively utilized seismic and inversion data, analyzed the best threshold value for distinguishing the gas hydrate in the study area and, on such a basis, quantitatively interpreted the gas hydrate. The results obtained show that:First,the velocity of gas hydrate is about 2050~2150 m/s, and P?impedance is above 3.9 × 106kg·m-3 ·m·s-1 in the study area,which are higher than the velocity and impedance of surrounding rock;Second,the distribution of gas hydrate is extensive, especially in the middle west and southeast region,where the preliminary estimated maximum thickness is up to 48m.