地震频谱衰减属性在松辽盆地南部深层火山岩气藏预测中的应用

The application of seismic spectral attenuation attribution in the prediction of deep-seated volcanic gas reservoirs in south Songliao Basin

松辽盆地南部深层火山岩气藏具有岩性复杂、非均质性强的特点。受地震资料分辨率和信噪比的限制,采用地震振幅属性和地震相分析等技术手段预测含气性的效果较差。地震频谱衰减属性可以反映地层的吸收性质、岩相和含气性,利用含气层段对地震波高频能量吸收强的特点,可以较好地预测含气层段。采用最大熵谱算法计算储层的谱率,预测低谱率部分可能含气;同时,采用该算法计算储层上、下一定时窗内地层频谱的比值,获得频谱衰减剖面,预测高频衰减强烈层段为含气层。这2种预测方法相互结合可以有效降低含气预测的多解性。实际应用也证明用地震频谱衰减属性预测含气性是行之有效的。

The deep-seated volcanic gas reservoirs in south Songliao Basin have both complex lithology and strong areal heterogeneity characteristics. Generally,restricted by the signal-to-noise ratio and resolution of seismic data,the gas distribution prediction has poor effect with techniques of amplitude attributes and seismic facies analysis.The seismic attribute of frequency spectrum attenuation can reflect strata properties such as absorption,lithofacies and gas bearing.Gas-bearing formation can be predicted according to the characteristics that the high frequency energy of seismic wave can be absorbed strongly when reservoirs contain gas.The method of computing maximum entropy spectrums can calculate the spectral ratio and can predict gas-bearing intervals at low spectral ratio part,and also can be used for calculating the ratio of frequency spectrum within the windows of overlying or underlying the target.Spectral attenuation profile can be obtained and prediction degree can be upgraded by searching high frequency attenuation intervals.The combination of the two solutions will decrease the ambiguity of gas-bearing identification.The practice has proved that the seismic attribute of spectrum attenuation is an effective method for gas-bearing reservoir prediction.