Shear-wave velocity ( V S ) 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 ( I P ) among tight sandy conglomerate, tight siltstone, and mudstone are negligible, and the V P / V S exhibits substantial overlap. Rock physics analysis identifies V S as the most sensitive elastic parameter in the SQ4 of this area. The relatively low accuracy of previous reservoir predictions leads to a drilling success 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 V S ) 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 V S values. Compared with the second method, the first method reduces the inversion error from 25% to 10%. Moreover, the relative V S values outperform the relative P-wave impedance in distinguishing lithology and identifying sweet-spot reservoirs. After residual multiple attenuation is applied to the actual quasi-pure wave gathers, the direct V S inversion results from full-offset gathers in the target interval (SQ4 member of the Shahezi Formation) show good consistency with the drilling results of Well BSH9H. Three subsequent wells drilled in predicted high-quality reservoir zones yield high industrial gas flow exceeding 1 million cubic meters per day, whereas one well located in a predicted low-quality zone produces only low gas flow.
Sun et al. (2026) studied this question.