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二氧化碳注入地层驱油过程中会引起地震波速度的频散现象,这是地震波传播过程中相速度随频率发生变化所造成的。所以综合考虑二氧化碳气驱情况下的速度频散效应,提取频散因子,进而动态监测气驱前后的油藏变化,具有方法的可行性。本文从Robinson频散褶积模型出发,首先推导了速度频散因子的定量表征式,构建了含有速度频散因子的反演方程,给出了四个处理步骤的实现过程,其中包括广义S变换谱分解、井旁道子波提取、谱均衡处理和阻尼最小二乘频散因子提取。根据粘弹性介质理论,建立了基于Q值变化的衰减地层模型,对止演后的偏移剖面进行了时频谱分析,在此基础上进行了频散因子提取与对比,验证了方法的有效性。最后,将本文方法应用到胜利油田高89井区注气前后两期资料的目标处理与驱油监测中。从提取的两期地震频散因子剖面和切片来看,方法能较好地指示二氧化碳驱前后的差异性,研究成果与井场实际考察结果非常吻合。
Displacement of seismic wave velocity caused by CO2 injection into the formation during oil displacement is caused by the change of the phase velocity with frequency during the seismic wave propagation. Therefore, taking into account the velocity dispersion effect in the case of carbon dioxide gas flooding and extracting the dispersion factor, and then dynamically monitoring the reservoir changes before and after gas flooding, the method is feasible. Based on the Robinson frequency dispersion convolution model, this dissertation first derives the quantitative representation of velocity dispersion factor, constructs the inversion equation with velocity dispersion factor and gives the realization of four processing steps, including generalized S transform Spectral decomposition, wavelet extraction of well bypass, spectral equalization and damping least-squares dispersion factor extraction. According to the theory of viscoelastic medium, the attenuation stratum model based on the change of Q value is established, and the time-frequency spectrum analysis is performed on the offset section after staged performance. On this basis, the dispersion factor is extracted and compared, and the validity of the method is verified . Finally, the method of this paper is applied to the target treatment and oil displacement monitoring of two data before and after gas injection in Gaox 89 well of Shengli Oilfield. The results show that the proposed method is a good indicator of the difference between before and after carbon dioxide flooding. The research results are in good agreement with the actual field observations.