Fluid Prediction Based On Prestack Geostatistical Inversion

Compared with poststack inversion,prestack elastic inversion can obtain favorable reservoir spatial distribution characteristics for rock elastic parameter volume prediction under seismic resolution.These data volumes are faithful to seismic response,but their vertical resolution is limited by seismic resolution,and it is difficult to distinguish single sand body whose thickness is much smaller than seismic resolution.Prestack geostatistical inversion of longitudinal and shear wave velocities on input wells,calculation of corresponding longitudinal and shear wave impedance through seismic synthetic records,constraints of geological framework model,prestack seismic data and geological trend,and random simulation algorithm are used to obtain a series of high-resolution data volume of reservoir sensitive parameters,taking into account the vertical resolution of logging data and the lateral resolution of seismic data.Therefore,thin-bed and thin-interbed reservoirs can be identified better on the basis of prestack deterministic inversion.In order to meet the urgent requirement of oil and gas development and remaining oil potential tapping in the study area,this paper uses prestack depth domain geostatistical inversion technology to predict oil saturation,and predicts remaining oil area from qualitative to quantitative.The inversion results are in good agreement with the logging data and accord with the geological knowledge.The redistribution of sand body in the study area is re-recognized based on the prediction results,which is a reliable basis for determining the key areas of remaining oil development.Shear wave data is a key factor in prestack inversion.However,there are few or even missing shear wave data in every research area in actual production.It is a widely used shear wave prediction technology to reconstruct shear wave information from conventional logging data.On the basis of comprehensive research and analysis,the S-wave velocity prediction of all wells in the study area has been completed by least squares fitting polynomial method.The comparative analysis of six S-wave logging curves in the study area shows that the average coincidence rate between predicted and measured S-wave is over 96%.The prediction accuracy of S-wave data can be effectively used in prestack inversion calculation of seismic data.Based on the predicted shear wave velocity,a low-frequency model is established,and the pre-stack simultaneous inversion and prestack geostatistical inversion trial calculation are completed.The elastic parameter data and logging data obtained from the inversion are compared and analyzed.The results show that the elastic parameter prediction results obtained from the inversion are in good agreement with the well data.The calculation shows that the method can be popularized and applied in the study area of similar reservoirs.Geostatistical inversion effectively integrates high-frequency logging information,greatly improves the vertical recognition ability,respects actual drilling data at well points,and can more objectively and truly reflect reservoir sedimentary characteristics.Based on the petrophysics of well point and the analysis of inversion results,it is considered that the density elastic parameters can describe the reservoir sand body well,and the vertical recognition ability of thin sand body is strong.On the basis of relatively accurate prediction of reservoir sand body,water saturation of physical parameters and density of elastic parameters are used to obtain water saturation data of reservoir fluid description through statistical analysis of probability distribution.Finally,the remaining oil distribution and content of seven reservoir groups are predicted.The average error is less than 15%,and the prediction accuracy is high.Combined with inversion profile analysis,the remaining oil in the study area is mainly distributed in the up-thrown side of fault,so the up-thrown side of fault is an important target area for further tapping potential.