Abstract: Reservoir prediction of tight sandstone is always a difficult problem in the industry. Conventional post-stack impedance cannot distinguish between dense surrounding rock and high porosity sandstone effectively, and such problem is particularly typical in the study of tight sandstone reservoir prediction of Xujiahe Formation in Dayi Area, western Sichuan. To solve such problems, this paper carried out research by pre-stack technology. The petrophysical analysis shows that the velocity ratio of P-wave and S-wave has a good distinguishing effect on porous sandstone reservoirs, which indicates that the pre-stack technique can effectively solve the prediction problem. The properties of P-wave impedance, S-wave impedance and the velocity ratio between P-wave and S-wave are obtained by pre-stack inversion. With the help of lithofacies analysis technology, the sweet spot probability body of pore sandstone reservoir is generated, and the plane distribution of pore reservoir is predicted. The results show that the technique is effective and consistent with real drilling, which is of great significance to the exploration and development of tight sandstone field. This paper also elaborates the key technical links of pre-stack prediction, which included pre-stack optimization, partial stacking, petrophysical analysis, probabilistic model building, inversion calculation, and effect analysis of real drilling comparison. Each key link is critical to the reliability of the results. This method provides strong technical support for the study of tight sandstone reservoir prediction and has important guiding significance for continental exploration in western Sichuan.

Key words: tight sandstone, pore reservior, prestack inversion, $v_{\rm p}/v_{\rm s}$, probability density function