Seismic response variation of tight gas sand for uniform and patchy saturation patterns

• We calculate velocity–saturation relationship in uniform and patchy saturation patterns.
• We analyze the variations of AVO response and attribute induced by saturation patterns.
• Patchy saturation in tight sand is more helpful for gas content evaluation.

When tight sand reservoir is gas–water saturated the distribution pattern of mixed fluid will lead to different velocity–saturation relationships, which will eventually cause the variation of seismic response. Assuming the gas–water mixed fluid in tight sand is uniform saturation or patchy saturation, theoretical velocity–saturation relationships are calculated by using the Gassmann equation and patchy equation respectively. Based on the two trends of velocity, we built a numerical model and analyzed the variations of AVO response, AVO attribute and prestack inversion by using numerical simulation results. The AVO analysis and prestack inversion results all show that when tight sand reservoir is gas–water saturated patchy saturation is more conducive to the prediction of gas content.