子波提取

子波提取

褶积模型是所有反演的基础:

地震道=地震子波*反射系数+噪声

频率域内, 褶积则为乘积的关系.

反演相当于地震道除以地震子波, 得到反射系数:

反射系数=地震道/地震子波

频域内窄频段的子波限制了信息的获取范围.The narrow band wavelet restricts the available range of information in the frequency domain.

地震子波完全由它的振幅谱和相位谱来定义:

The Wavelet is defined completely by its amplitude

spectrum and its phase spectrum:

在有限频率范围内, 相位谱通常可近似为一条直线. 直线的截距是子波的常数相位旋转, 它是子波的最佳表征. 直线的斜率标示着子波的时移.

The intercept of the line is the constant phase rotation which best characterizes this wavelet.

The slope of the line measures the time-shift of the wavelet.

极性的约定:

极性约定是一个特殊的子波相位问题. 默认的约定便是: 声阻抗的增加在零相位的地震数据上代表一个波峰.

A special wavelet phase issue is the Polarity convention.

The default convention is that an increase in acoustic impedance is represented as a peak on zero-phase seismic data:

另一个默认的约定便是: 声阻抗的增加在零相位的地震数据上代表一个波谷.

The alternate convention is that an increase in acoustic impedance is represented as a trough on zero-phase seismic data:

使用ì极性约定菜单î可以设置极性约定:

The polarity convention is set using the Synthetic

Polarity Convention menu:

地震子波在时间和空间上都存在着变化, 即具有时变性和空变性, 这是基于以下几个原因:

Wavelets in the earth vary both laterally (spatially) and temporally for a variety of reasons:

近地表效应(空变)

Near surface effects (space variant)

频率吸收(时变和空变)

Frequency-dependent absorption (space and time variant)

层间多次波(时变和空变)

Inter-bed multiples (space and time variant)

NMO 拉伸

处理过程中的人为因素

Processing artifacts

STRATA 假定子波是常数, 不随时间和空间变化: 时间不变性: 这意味着反演就是在有限的时窗内求最优化的波阻抗

Time invariant: This means that the inversion is optimized for a limited time window.

空间不变性: 这意味着去除子波的空变后被最优化处理. 通常, 许多方法有可以用来提取子波. STRATA中用了以下几种:

In general, a variety of methods can be used for wavelet extraction. Some are available in STRATA. (1) 仅用地震数据估计地震子波的振幅谱. 假设相位谱已经从别的渠道得知.

子相关autocorrelation

最大熵谱分析maximum entropy spectral analysis

交互谱分析cross spectral analysis

STRATA中统计子波的提取用自相关: Statistical wavelet extraction uses the autocorrelation

(2) 单独使用地震数据估算振幅谱和相位谱

Estimate both amplitude and phase spectra from the seismic data alone.

最小熵子波估计

高阶力矩法higher order moments

STRATA 不用这种方法, 因为STRATA认为该方法不可靠.

(3) 使用给定的测量数据估计振幅谱和相位谱

Estimate both amplitude and phase spectra using deterministic measurements.

海洋信号marine signatures

VSP 分析

STRATA中, 以ASCII文件形式读入外部子波

(4) 用地震和测井资料估算振幅谱和相位谱

Estimate both amplitude and phase spectra using both seismic and well log measurements.

STRATA中用测井资料提取全子波.

(5) 用地震资料和测井资料估算振幅谱和常数相位谱STRATA中用测井资料提取常数相位子波.

STRATA中提取子波的方法:

第一步, 是否用测井资料来估算子波的相位. 关键是看测井资料与地震资料的相关性是否好. 通常情况下, 必须首先进行手动校正测井曲线. The critical issue for this decision is how well the logs tie the seismic data. Usually, manual correlation must be done to align the logs first.