基于BISQ机制的双相EDA介质的波场分析

Wavefield analysis of biphase EDA medium based on BISQ mechanism

本文应用高精度交错网格有限差分法,实现了基于BISQ机制的单层双相EDA介质波场模拟、三层双相介质地面地震记录模拟,分析了在地震频带内双相介质理论与单相弹性介质理论在解释地震波传播时的差异及影响慢纵波的因素。得出以下认识:①基于BISQ机制的双相EDA介质中的地震波场的地面地震模拟结果表明,这类介质中存在第二类纵波(慢纵波),慢纵波的速度与孔隙率、流体密度成正比,与耦合密度成反比,而其振幅一般与孔隙率成反比。②在给定相同参数的情形下,BIOT理论、BISQ理论、单相弹性理论所描述的地震波场的传播现象是相似的,同双相BISQ理论相比,BIOT理论和单相弹性理论都低估了地震波的衰减,高估了地震波的频散,这说明BIOT理论存在不足;从地震波的到达时刻来看,在地震频带内(即低频范围),单相弹性理论和BIOT理论预测的各种波的速度较BISQ理论预测的各种波的速度高,到达时刻也早。目前认为基于BISQ机制的双相介质模型更符合实际情况,应用BISQ正演模拟技术可提取储层参数。

Using high-precision staggering mesh finite-difference approach, the paper finished wavefield simulation of biphase one-layer EDA medium based on BISQ mechanism and surface seismic records simulation of biphase triple-layer medium, and analyzed the difference in interpretation of seismic wave propagation between biphase medium theory and single-phase medium theory within seismic bands and the factors affecting slow P-wave, which gained following knowledge: the results of surface seismic simulation of seismic wavefield propagating in biphase EDA medium based on BISQ mechanism showed there exists second mode of P-wave (slow P-wave), the velocity of which is in proportion to porosity and fluid density, and an inverse measure of coupled density; the amplitude of which is generally inversely proportional to porosity. In a case of given same parameters, the propagation phenomenon of seismic wavefield described by BIOT theory, BISQ theory and single-ghase elastic theory is similar; in comparison with biphase BISQ theory, the BIOT theory and single-phase elastic theory underestimated the attenuation of seismic waves and overestimated the dispersion of seismic waves, which showed the shortcoming of BIOT theory. Seen from arrived times of seismic waves, within the seismic band (i.e. low frequency range), the velocities of various waves predicted by single-phase elastic theory and BIOT theory are higher than that by BISQ theory, and earlier for arrived time. Currently, it is considered that the biphase medium model based on BISQ mechanism is more consistent with the practical situation and application of BISQ forward simulation technique could detect reservoir parameters.