叠前反演和地震吸收技术在复杂天然气藏地震预测中的应用

Application of pre-stack seismic inversion and seismic absorption technology for forecasting of complex gas reservoir

针对某复杂断块天然气目标储层,在岩石物理分析的指导下,综合利用地质、地震、测井等资料,提出了一套面向复杂天然气藏的叠前地震预测技术.首先基于地震岩石物理分析得到的初始横波信息,采用叠前贝叶斯非线性三参数反演得到了井旁控制点处精确纵横波速度和密度信息,然后通过叠前/叠后联合反演技术实现了面向目标的弹性阻抗体反演及含气储层敏感参数直接提取,最后结合小波变换时频谱分析的方法从叠前地震资料中估算地层吸收参数值,提高天然气藏识别精度.实际应用表明,综合各种叠前地震预测技术,可以大大提高对复杂天然气藏的识别精度,降低勘探风险.

Pre-stack seismic data plays an important role in reservoir forecasting in exploration seismic and reservoir description in development seismic. Some elastic parameters form pre-stack seismic inversion has been proved to be sensitive to reservoir and fluid, further more, seismic absorption parameter as a strong fluid factor indication also has been proved as be effective in gas reservoir forecasting, therefore, a procedure for complex gas reservoir with a series of pre-stack seismic technologies based on comprehensive analysis with geology, seismic, well logging and rock physics data is proposed. Two main seismic technology including pre-stack seismic inversion and seismic absorption have been applied in this procedure. On one hand, for the technology of pre-staek seismic inversion, the shear velocity at control points near well locations could be estimated from rock physics preliminary, and then it can be inverted more accurately with the method of pre-stack nonlinear AVO inversion, in addition, the elastic parameters which are sensitive to target reservoir are inverted with control of seismic rock physics and well logging data utilizing post/pre-stack hybrid inversion technology, the post/pre-stack hybrid inversion technology is a kind of pre-stack seismic inversion method with partial angle stack gathers, which has shown great potential in application of reservoir description and forecasting for its efficiency and robustness. On the other hand, for the technology of seismic absorption parameter extracting, the method of estimating absorption parameter from pre-stack seismic data has been applied. Compared with pos-stack seismic data, pre-stack seismic contains more helpful kinematics and dynamics information compared with post-stack seismic data, therefore the absorption parameter is extracted from pre-stack seismic data will be more accurate, this method is implemented with wavelet time-frequency spectrum analysis which aims to enhance the preciseness of reservoir forecasting. Field example showst hat the new combined technology procedure performs well for the forecasting of complex gas reservoir.