地震信号的多尺度频率与吸收属性

利用小波函数具有良好的时间域与频率域局部化特征, 在不同尺度下, 对地震数据进行小波变换, 能够有效地提取地震信号的时间-频率分布特征。基于小波理论, 对Aki & Richards(1980)给出的地震波振幅公式进行连续小波变换, 推导出地震波传播时间、频率与吸收系数之间的关系。进而, 计算出地震信号的吸收属性, 有效凸显地震信号主频低、高频缺失严重、反射弱、反射空白、反射杂乱、波形肥胖等含油气响应特征。含烃储集层对高频成份具有特殊的响应, 并时常伴随有强烈的地震波振幅、能量与频率吸收衰减, 在不同尺度下计算地震波的主频、吸收系数能够有效地反映地震波的频移与吸收衰减特征, 有利于岩性识别、油气预测及综合解释。将该方法运用到川西坳陷深层须家河组致密碎屑岩含气性预测中, 预测的异常区块与区内测井结果吻合良好。

Multi-Scale Frequency and Absorption Attributes of Seismic Signals

Based on wavelet theory, this paper obtained the multi-scale dominant frequency (MSF)by using wavelet analysis, and derived a new relationship algorithm between travel-time, frequency and absorption coefficients from transforming the seismic amplitude equation proposed by Aki & Richards (1980), then calculating the multi-scale absorption attributes (MSA)of seismic signals in time-frequency domain, which effectively show the oil and gas response characters, such as low main frequency, serious high frequency absence, dimming reflection, reflection blank, reflection disorder and fat wave shape. Hydrocarbon reservoir has special response to high frequency sects, and goes with intensive amplitude, energy and frequency absorption of seismic waves. Calculating MSF and MSA of seismic data at different scale can reveal frequency shift and absorption attenuation characters of seismic waves, which is favorable to lithology identification, petroleum reservoir prediction and synthetic interpretation. A case study of MSF and MSA techniques applied to seismic data from dense clastic rocks of Xujiahe formation in depression of western Sichuan basin provides robust indications for reservoir prediction and gas detection.