砾岩储层地震波传播方程:三重孔隙结构模型

针对砾岩储层的砂、砾、泥三重孔隙结构特征,本文分析砾岩孔隙区域、砂岩孔隙区域以及泥岩孔隙区域相互之间的孔隙流体流动机制,将静态的砾岩骨架本构方程与动态的孔隙流体运动方程联立,提出了复杂砾岩储层的弹性波传播理论方程.采用实测砾岩储层参数,在算例中与双重孔隙介质理论进行对比分析,验证了本文理论方程的合理性;基于三重孔隙介质模型,分析不同储层环境下纵波的传播特征,结果显示:随流体黏滞系数增大,在衰减-频率轴坐标系中,砾与砂、砂与泥孔隙区域间局域流导致的两个衰减峰向低频端移动,而Biot全局流导致的衰减峰向高频端移动;嵌入体尺寸及背景相介质渗透率的变化,主要影响纵波速度频散曲线沿频率轴左、右平移,不影响波速低频、高频极限幅值;嵌入体含量及孔隙度的变化改变了岩石干骨架的弹性、密度参数,不仅影响速度频散曲线沿频率轴平移,而且影响其上、下限幅值;砾包砂包泥三重孔隙介质模型所预测的衰减曲线中,低频段"第一个衰减峰"主要由砾岩孔隙区域与砂岩孔隙区域之间的局域流导致,中间频段"第二个衰减峰"主要由砂岩孔隙区域与泥岩孔隙区域之间的局域流导致,超声频段"第三个衰减峰"由Biot全局流导致.对慢纵波传播特征的分析显示,砂岩骨架(局部孔隙度较大)内部的宏观孔隙流体流动造成的耗散明显强于砾岩与泥岩骨架.

Seismic wave propagation equations of conglomerate reservoirs: A triple-porosity structure model

According to the triple-porosity structure characteristics of conglomerate, sand and mud composite in conglomerate reservoirs, this paper analyzes the mechanisms of pore fluid flow among the conglomerate, sandstone and mudstone pore systems. By combining the static constitutive equations of the conglomerate skeleton and the dynamic motion equations of pore fluid, we propose the theoretical equations of elastic wave propagation in complex conglomerate reservoirs. Employing the measured conglomerate reservoir parameters, the rationality of the theoretical equations in this paper is verified by the analysis and comparison with the double-porosity media theory in numerical examples. Based on the triple-porosity model, we analyze the wave propagation characteristics of P-waves in different reservoir conditions. Results show that with the increasing fluid viscosity, the two wave attenuation peaks generated by the local flow between conglomerate and sandstone and sandstone and mudstone pore systems shift to the low-frequency end in the attenuation-frequency coordinate system, and the attenuation peak caused by Biot global flow shifts to the high-frequency end. Changes in the size of inclusions and the permeability of host media mainly affect the P-wave velocity and dispersion curves shifting left/right along the frequency axis, and will not affect the amplitude of wave velocity in its low/high frequency limits. Variations in the volume ratio of inclusions and porosity change the elastic and density parameters of rock skeleton, which will not only affect P-wave velocity dispersion curves shifting along the frequency axis, but also affect the amplitude of wave velocity limits. In the attenuation curves predicted by the "mudstone embedded in sandstone embedded in the conglomerate" triple-porosity model, the first attenuation peak at the low frequency end is mainly caused by the local fluid flow between the conglomerate and sandstone pore systems, the second attenuation peak at the intermediate frequencies is mainly caused by the local fluid flow between the sandstone and mudstone systems, and the third attenuation peak at the ultrasonic frequencies is mainly caused by the Biot global flow. Analysis on the characteristics of slow P-wave propagation also shows that the dissipation caused by the global fluid flow in the sandstone system (which has a higher local porosity) is obviously stronger than that in the conglomerate or mudstone system.