全炮检距道集横波速度叠前反演在储层预测中的应用OA

Shear-wave velocity(VS)plays a crucial role in the prediction of clastic rock reservoirs,including the identification of"sweet spots".In the Shahezi Formation of the Xujiaweizi BSH9 well area,the differences in P-wave impedance(IP)among tight sandy conglomerate,tight siltstone,and mudstone are negligible,and the VP/VS exhibits substantial overlap.Rock physics analysis identifies VS as the most sensitive elastic parameter in the SQ4 member of this area.The relatively low accuracy of previous reservoir predictions leads to a drilling suc-cess rate below 80%for sandy conglomerate reservoirs in the SQ4 member,as well as poor prediction accuracy for high-porosity and high-permeability"sweet spots".This is a key reason for the low productivity of earlier wells such as BSH1 and BSH5.Based on single-interface model data at the top of the reservoir and well-log data(including VS)from the target interval,AVO forward modeling is performed to generate common reflection point(CRP)gathers.Two pre-stack inversion methods,full-offset-gather pre-stack inversion and partial-stack pre-stack inversion,are applied to these gathers to obtain relative VS values.Compared with the second method,the first method reduces the inversion error from 25%to 10%.Moreover,the relative VS values outperform the relative P-wave impedance in distinguishing lithology and identifying sweet-spot reservoirs.After residual mul-tiple attenuation is applied to the actual quasi-pure wave gathers,the direct VS inversion results from full-offset gathers in the target interval(SQ4 member of the Shahezi Formation)show good consistency with the drilling re-sults of Well BSH9H.Three subsequent wells drilled in predicted high-quality reservoir zones yield high indus-trial gas flow exceeding 1 million cubic meters per day,whereas one well located in a predicted low-quality zone produces only low gas flow.