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Organic reef reservoirs in the platform margin of Kaijiang-Liangping trough in Damaoping area, Sichuan Basin are thin in single layer, fast in lateral variation, and have small P-impedance difference from the surrounding rock, it is difficult to identify and predict the reservoirs and fluid properties by conventional post-stack inversion. Through correlation analysis of core test data and logging P-S wave velocity, this work proposed a formula to calculate the shear wave velocity in different porosity ranges, and solved the issue that some wells in the study area have no S-wave data. AVO forward analysis reveals that formation porosity is the main factor affecting the variation of AVO type, the change of water saturation cannot affect the AVO type, but it has an effect on the change range of AVO. Through cross-plotting analysis of elastic parameters, it is found that fluid factor is a parameter sensitive to gas-bearing property of organic reef reservoir in the study area. By comparing results of post-stack impedance inversion, post-stack high frequency attenuation property, pre-stack simultaneous inversion and AVO anomaly analysis of angle gathers, it is found that the gas-bearing prediction of organic reef reservoirs by using fluid factor derived from simultaneous pre-stack inversion had the highest coincidence rate with actual drilling data. At last, according to the characteristics of fluid factor distribution, the favorable gas-bearing area of the organic reef reservoir in Changxing Formation was predicted, and the organic reef trap at the top of Changxing Formation in Block A of Damaoping area was sorted out as the next exploration target. Key words: Sichuan Basin, Permian Changxing Formation, organic reef, prestack inversion, S-wave estimation, rock physics, fluid factor, gas detection

Based on the slope theory in geomorphology, a method, which can identify the boundary of platform reef by high precision slope attribute calculation based on the horizon data of fine seismic interpretation, combining the ancient geomorphic analysis method, was established. The conventional seismic prediction methods, drilling results and the thickness data of Changxing Formation were used to verify and supplement this method. Then, this method was used to identify the boundary of uplifted reef on the planar image in the Permian Changxing Formation in Luodingzhai area of Sichuan Basin. The results show that the reef boundary imaged by this method is consistent with the reef distribution revealed by the drilling, and is clearer in local details. Compared with conventional seismic prediction methods, the reef boundary identified based on the same fine seismic horizon interpretation results by this method has no multiple solution on the planar image. Key words: Sichuan Basin, Permian Changxing Formation, reef, seismic interpretation, slope, boundary identification