摘要
Frequency attenuation occurs when seismic waves propagate through the porous reservoirs containing hydrocarbons. Current researches on the seismic frequency attenuation mainly focus on the post-stack domain instead of the prestack domain. Here we propose the frequency attenuation gradient vs. offset （FAGVO） based on the amplitude variation with offset and frequency attenuation integral equations. We derive the FAGVO equation that equals to zero in a full-elastic medium and is negative in a viscoelastic medium. FAGVO is affected by the viscosity of the medium, the coefficients of reflection, the frequency variation, and high-frequency attenuation. FAGVO uses the differences of partially stacked data to decrease the interference caused by subsurface strata affecting the frequency attenuation, highlights the frequency attenuation gradient anomalies in hydrocarbon-bearing reservoir pores, and finally realizes the hydrocarbon fluid identification. The method was verified using a two-dimensional wave equation forward model and was found to be cost effective. Furthermore, the method does not require well information, which can be applied in the stage of seismic exploration, especially, in the exploration of a none-well project.
地下储层含烃类流体引起地震信号频率的衰减,目前对叠后地震资料的频率衰减研究较多,但是涉及叠前道集上的频率衰减研究较少。作者综合叠前AVO的计算公式及频率衰减积分计算式,对叠前部分叠加角道集的频率衰减梯度差值(Frequency Attenuation Gradient vs.Offset,简称FAGVO)的计算公式进行了推导,显示完全弹性介质的FAGVO为零,粘弹性介质的FAGVO为负值,且FAGVO的绝对值大小与介质粘度、频率变化、反射系数及高频的衰减有关。FAGVO可以消除部分影响地下岩层频率变化因素的干扰,从而突出含烃储层频率衰减梯度的异常,达到利用叠前部分叠加道集进行含烃类流体检测的目的。该方法经过二维波动方程正演模型的验证,检测效果理想,且该方法对钻井信息的依赖较小,可应用于油气地震勘探阶段,尤其是无井区的勘探,既经济又高效。
基金
supported by the Major National Science&Technology Project(No.2016ZX05003-003)
the National High Technology Research and Development Program of China(863 Program)(No.2013AA064201)
