基于affine类时频分析的旋回性薄互层时频特征影响因素分析

A time-frequency feature analysis of cyclic thin interbeds based on time-frequency analysis of affine class

affine类时频分析方法具有模糊瞬时频谱变化细节,突出主要频率变化趋势的特点,具有较好的旋回判别能力,因而被学者用于旋回性薄互层类型判别当中,研究发现,旋回性薄互层时域波形均有向薄层方向波形密集,厚层方向波形稀疏的特点,但其稳定性差,易受外界干扰影响。由仿射类时频分布得到的时频谱与沉积旋回模式具有一一对应关系,不同模式旋回薄互层均有向层厚减薄方向的升频特点,目前关于旋回性薄互层时频特征影响因素的研究很少,厘清这些因素对旋回判断准则的影响有重要的意义。基于以上考虑,本文以正旋回模型为基础,从小层厚度突变、波阻抗大小、噪声影响、地震资料主频大小、地层黏性吸收作用等5个方面对旋回判别的影响进行了探讨。首先根据波动理论,利用深度域相移法对不同影响因素条件的旋回性薄互层进行正演模拟,分别抽取零偏移距道集进行仿射类时频分析,对比理想情况的旋回性薄互层时频特征差异。结果表明:仿射类时频分布判别沉积旋回抗噪能力强,受薄互层中小层厚度轻微突变的影响小;波阻抗的变化主要影响时频谱时间方向能量分布,对频率方向能量分布影响甚微;地震资料主频变化对时频特征的影响较小,随着地震资料主频的增加,旋回的趋势更加明显;地层黏性吸收作用对该方法判别的准确度影响也较小,时频特征稳定。

The affine time-frequency analysis method has the characteristics of fuzzy instantaneous spectral changes,highlights the characteristics of the main frequency variation trend,and has a good capability for determining the degree of cycle.Therefore,it has been used by experts in the classification of cyclic thin interbed types.The layer time domain waveforms are characterized by dense waveforms toward the thin layer and sparse waveforms in the thick layer direction,but their poor stability is susceptible to external interference.The time-spectrum obtained from the affine class time-frequency distribution has a one-to-one correspondence with the sedimentary cycle pattern.The frequency rising characteristics of thin interbeds in different model cycles are in the direction of thickness thinning.As the study of the influencing factors of cyclic interbeds characteristics in the current time is very insufficient,it is important to clarify the influence of these factors on the criterion of the cycle.Based on the above considerations,this paper discusses the influence of the sudden change in the thickness of the small layer,the size of wave impedance,the influence of noise,the size of seismic data frequency and the viscous absorption of the formation on the cycle discrimination based on the positive cycle model.Firstly,according to the wave theory,the depth-domain phase-shift method is used to make forward simulation of the cyclic thin interbeds with different influencing factors,and zero-offset gathers is extracted for affine time-frequency analysis;after that,the differences of time-frequency characteristics of cyclic thin interbeds are compared under ideal conditions.The results show that affine time-frequency distribution has a strong capability for discriminating sedimentary cycles against noise,and is less affected by slight sudden changes in the thickness of thin interbeds,that the variation of wave impedance mainly affects the temporal energy distribution of time-frequency spectrum,but has little effect on the energy distribution of frequency-direction,and that the variation of main frequency of seismic data has little effect on the time-frequency characteristics,whereas the variation of main frequency of seismic data has little effect on the time-frequency characteristics.With the increase of main frequency of wave,the trend of cycle is more obvious,the influence of stratigraphic viscous absorption on the accuracy of this method is also small,and the time-frequency characteristics are stable.