The conversion of fast to slow diffusion P waves in fluid-saturated porous media induces attenuation and dispersion of waves at seismic frequencies. This effect, known as wave-induced fluid flow, occurs at mesoscopic scales, which are much larger than the average pore size and much smaller than the average fast P-wave wavelength. When analyzing this mechanism in hydrocarbon reservoirs with the pore space saturated by multiphase fluids, it is important to include capillary pressure effects and flow interaction between fluids, which cause additional attenuation and velocity dispersion of P waves. We have developed a procedure to determine the phase velocities and dissipation factors in a medium composed of a periodic sequence of three poroelastic thin layers saturated by two-phase fluids. The methodology consists of applying compressibility tests to representative samples of the material, which are defined as boundary-value problems solved using a finite-element procedure. First, we analyze the case of two-phase fluid saturation on each layer, and the results are compared with those of the single-phase (effective) fluid case. Then, several cases of patchy saturation are presented, indicating that residual and wetting fluid saturation play an important role in determining the P-wave velocities and dissipation factors.

中文翻译：

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两相流体饱和的三层薄层周期序列的地震响应

流体饱和多孔介质中快速扩散到慢速扩散 P 波的转换会引起地震频率下波的衰减和色散。这种被称为波浪诱导流体流动的效应发生在细观尺度上，该尺度远大于平均孔径，远小于平均快 P 波波长。在孔隙空间被多相流体饱和的油气藏中分析这种机制时，重要的是包括毛细管压力效应和流体之间的流动相互作用，这会导致 P 波的额外衰减和速度色散。我们开发了一种程序来确定介质中的相速度和耗散因子，该介质由两相流体饱和的三个多孔弹性薄层的周期性序列组成。该方法包括对材料的代表性样本进行可压缩性测试，这些样本被定义为使用有限元程序解决的边界值问题。首先，我们分析了每层两相流体饱和的情况，并将结果与​​单相（有效）流体情况下的结果进行了比较。然后，提出了几种不均匀饱和的​​情况，表明残余和润湿流体饱和度在确定纵波速度和耗散因子方面起着重要作用。