Prestack Inversion And Gas-water Identification Of The Changxing Formation Reefs In The Da Maoping Area

Daomaoping gas reservoir is to the east of KaiJiang-LiangPing trough with great exploration potential for Changxing reef to grow up in Platform edge facies.Two phases of reef were overlapped in the vertical,and every single reservoir is thin and varied rapidly laterally,researcher indicate that P-impedance of reservoir is so close to surrounding rock,Therefore,it is difficult to identify and predict reservoir position and fluid property by post-stack inversion.In this paper,we aiming at the problems of low signal-to-noise ratio seismic data and unleveled trace in study area,and start from pre-stack seismic data processing and adopt the method of "Denoise-Trim-Mute" based on "amplitude presentation",then the quality of seismic data can be improved,It is considered that P-wave and S-wave velocity relationship in the study area is closely related to porosity through the correlation analysis of core test data and logging P-S wave velocity.Therefore,we propose a formula about S-wave computing based on porosity interval,and the well without S-wave velocity data can be predicted.According to the statistical results of longitudinal and shear wave velocities and densities of reservoir and surrounding rocks,we make AVO forward model and conclude that there are two types of AVO in the top boundary of gas reservoir in the study area,the third type and the fourth type,while only the fourth type of AVO in the top boundary of water reservoir.Then we find out that reservoir porosity is the main factor leading to the change of AVO type in the study area and water saturation won't change the type of AVO,but will affect the range of AVO.At the same time,the intersection analysis of various petrophysical parameters shows that P-S wave velocity ratio is more sensitive to reef reservoir identification,and fluid factor ?? is more sensitive to gas-water identification in reservoir,and we respectively get the range of sensitive factors in surrounding rock,gas-bearing layer and water layer.Then we compare the similarities and differences of AVO attribute analysis.elastic impedance inversion and prestack simultaneous inversion and come to a conclusion that the simultaneous prestack inversion is the best way to predict reservoir with high coincidence rate between inversion results and downhole data,the distribution of effective thickness of gas reservoir in Changxing Formation can be obtained by the given fluid factor threshold value.Finally we get favorable exploration target areas of reef gas reservoir based on favorable sedimentary facies zones,seismic profiles and fluid factor ?? data of Changxing Formation in study area,this method has guiding significance for the reef gas reservoir prediction in Changxing Formation of the study area in Sichuan Basin.