Abstract: In view of the issue that conventional post-stack inversion fails to accurately predict the fluid in the reservoir, a pre-stack AVO fluid prediction method was used to analyze the petrophysical characteristics and AVO response characteristics of the dense sandstone in Qingshui Depression and to carry out a study on pre-stack fluid factor inversion. Petrophysical experiment was conducted to determine the elastic modulus of dense sandstones and the relationship between p-wave velocity and s-wave velocity of sandstone when the sandstones were saturated with fluids of different properties. Fluid substitution and pre-stack AVO analysis were also carried out. The results of the study showed that the density and Poisson′s ratio of dense sandstone in Qingshui Sag changed significantly under the condition of saturated oil, gas and water, especially after containing gas, the density and Poisson′s ratio decreased rapidly, and the AVO reflection amplitude decreased rapidly with increasing offset. This feature and the measured mudstone baseline were used to constrain the inversion of pre-stack AVO fluid factor, effectively improves the accuracy of oil and gas prediction in the tight sandstone of the area, laying a foundation for the accurate prediction of the oil-gas-water relationship in this area.

Key words: dense sandstone, petrophysics, fluid substitution, AVO inversion, fluid factor, reservoir prediction