基于饱水页岩地震频段岩石物理测试的地震响应频散特征分析

页岩储层由于骨架和孔隙结构的微观非均质性,能够在地震频段内引起波诱导的孔隙流体流动相关的弹性频散和衰减,但声波测井和实验室超声实验测量频率段远超地震频段,不可避免产生测量速度和衰减差异。这里基于澳大利亚惠灵顿地区的页岩岩心在干燥和水饱和条件下地震频段的弹性和衰减测量结果,考虑频变反透射系数和衰减对地震波反射的影响,针对不同层厚的页岩储层开展地震响应计算,并利用Wigner-Ville分布时频分析技术讨论了页岩频散、衰减性质及层厚对其地震响应规律的作用。对于无明显速度频散和衰减的页岩储层,顶、底反射振幅的频变属性受调谐效应控制,主要呈现出低频异常和陷频特征;而对于速度频散和衰减强烈的储层,顶、底反射振幅的频变属性同时受到调谐效应与储层本身频散衰减性质的作用。干燥和含水页岩储层地震响应的频变性质差异有助于加深对含流体页岩地震响应特征的理解,而基于地震频段实测数据正演和时频分析技术,对于提高页岩的地震勘探精度和流体识别具有重要的作用。

Analysis of seismic response dispersion characteristics based on rock physics test of water-saturated shale in seismic frequency band

Due to microscopic heterogeneity of the skeleton and pore structure,shale reservoir can induce wave-induced elastic dispersion and attenuation associated with pore fluid flow in seismic frequency band.But the frequency band measured by sonic logging and laboratory ultrasonic experiments far beyond the seismic frequency band.This paper is based on the measurement result of the seismic frequency band elastic and attenuation of a shale core taken from Wellington,Australia under dry and water-saturated conditions,considering the effects of frequency-dependent reflection and transmission coefficient and attenuation on seismic reflection wave.Seismic response calculations were carried out for shale reservoirs with different thickness,and the effects of shale dispersion,attenuation properties and layer thickness on seismic response were discussed by using Wigner-Ville distribution time-frequency analysis technique.For shale reservoirs with no obvious velocity dispersion and attenuation,the frequency-variation properties of the top-bottom reflection amplitude are controlled by the tuning effect,mainly showing low frequency anomalies and notching characteristics.But for reservoir with strong velocity dispersion and attenuation,the frequency-variation properties of the top-bottom reflection amplitude are simultaneously affected by the tuning effect and the dispersion attenuation properties of the reservoir itself.The difference in the frequency-dependent properties of seismic response of dry and water-saturated shale reservoir helps to deepen the understanding of seismic response characteristics of fluid shale.And the forward data and time-frequency analysis technique based on seismic frequency band have an important role in improving seismic exploration accuracy and fluid identification of shale.