Seismic prediction of reef in Changxing Formation of Gaofengchang Area,Eastern Sichuan Basin

In the end of the Permian period,Gaofengchang area is located in the disappeared transition zone of southeastern Kaijiang-Liangping trough as the gentle slope sedimentary environment.The thickness of Changxing Formation varies little in each sedimentary facies,so does the almost invariant formation thickness of reef developed area,which increases the difficulty of reef prediction.Early seismic data processing aims at multi-formations,which leads to mixed and disorderly seismic reflection of internal Changxing and eventually affects the accuracy of reef prediction.As a result,several reef exploration wells had failed in the area.Therefore,we carry out fidelity-preservation and amplitude-preservation fine processing on seismic data to improve the internal imaging effect in Changxing Formation.Meanwhile,we analyze the reef sedimentary facies and conclude their seismic responses.Model simulation indicates that the boundary of reef cannot be finely predicted by amplitude analysis at the top of Changxing Formation.Combining drilling analysis with seismic simulation results,aiming at the above deficiencies,the frequency-division interpretation technique is used on seismic data fine processed specifically for Changxing Formation which improves the accuracy of reef prediction.