叠前同步反演在徐家围子断陷火山岩气藏预测中的应用

徐家围子断陷营城组火山岩发育，天然气资源丰富，但火山岩储层的岩性非常复杂，气层与气水层之间存在严重的波阻抗叠置现象，基于全角度多次叠加地震资料的常规波阻抗反演不能给出反映物性和流体特征的参数，因此很难对火山岩气藏进行准确预测。但火山岩储层含气后，纵波速度降低，横波速度变化不大，基于这一特征，采用叠前同步反演技术，综合应用纵波弹性阻抗和纵横波速度比，可以对火山岩气藏进行识别。阐述了叠前同步反演的基本原理，讨论了反演处理中的地震资料处理、岩石物理分析、层位标定和子波提取、低频趋势模型建立等关键步骤。实际资料分析表明，低纵波弹性阻抗和低纵横波速度比对应含气火山岩储层，根据这一特点预测了有利含气区。

Application of pre-stack simultaneous inversion for predicting volcanics gas reservoirs in Xujiaweizi fault depression

Volcanic rock develops in Yingcheng group of Xujiaweizi fault depression,and abundant gas resource has been discovered in the volcanics reservoirs in this area.But the lithology of the volcanic reservoirs is highly complicated.Serious wave impedance overlapping phenomena exists between gas-bearing and gas/brine-bearing volcanics.Conventional wave impedance inversion based on all-angle multifold seismic data can not give the parameters reflecting physical properties and fluid features.So,volcanics gas reservoir is hard to be accurately predicted.When volcanics reservoir bears gas,its P-wave velocity decreases,but its S-wave velocity changes little.Based on this characteristic,combined with P-wave elastic impedance and vP/vS,pre-stack simultaneous inversion can be adopted to identify volcanics gas reservoir.The basic principles of pre-stack inversion was demonstrated,and the key steps in inversion were discussed,such as seismic data processing,rock physics analysis,horizon calibration and wavelet extraction,establishment of low-frequency trend model.Actual data analysis results show that low P-wave elastic impedance and low vP/vS indicates gas-bearing volcanic rock reservoir.According to this feature the favorable gas-bearing zones were predicted