不同孔隙流体下延长组砂岩波速各向异性的实验研究

利用Autolab 2000岩石物性测试设备，在0~200 MPa及三种不同孔隙流体条件下（干燥、水饱和及油饱和）研究了三种来自延长油田延长组的砂岩沿平行和垂直层面两个方向（即H和V）的纵波、横波速度，并分别计算了这些弹性波速的各向异性系数.结果表明：三种砂岩Y1、Y2和Y3两个方向上的V_P、V_SH和V_SV均随围压增加而基本呈对数函数形式变化，且纵波饱油曲线的斜率远大于饱水；Y1、Y2砂岩H方向的V_P、V_SH和V_SV在干燥、饱水和饱油条件下基本上均大于对应的V方向的波速；干燥、饱水和饱油条件下Y1、Y2的波速各向异性系数ε、γ和ζ和围压之间呈指数或二次函数降低；Y1、Y2、Y3三个岩样之间的速度各向异性差异明显，以Y2的各向异性最显著，其次是Y1，而Y3基本没有各向异性.另外，Y1、Y2的各向异性系数ε、γ和ζ之间表现出明显的与压力和流体状态相关性，且在实验压力范围内，饱油条件下的ε、γ均大于对应的饱水条件.实验结果可以为该地区地震资料的解释、油水层划分及与声波测井之间的对比提供重要的基础数据.

An experimental study of P- and S-wave velocities anisotropy in sandstones filled with differential pore fluids from the Yanchang Formation

This work applied AutoLab 2000 computer-controlled servo hydraulic triaxial test system to measure accurate P- and S-wave velocities at pressures up to 180 MPa on three kinds of core samples of sandstones that were cut parallel and perpendicular to the bedding planes (i.e., H and V) in dry, water and oil-saturated conditions from the Yanchang Formation in the Yanchang oilfield, and the wave velocity anisotropy parameters were also calculated. The results show the wave velocities V_P. V_SH, and V_SV for all H and V samples cut from three kinds of samples of sandstone Y1,Y2 and Y3 change basically logarithmically with increasing confining pressure p, and for all V_P, the slopes of the oil-saturated curves are greater than those of the corresponding water-saturated curves;for all H samples, in dry, water- and oil-saturated conditions the V_P, V_SH, and V_SV are larger than the corresponding ones for V samples;for two kinds of sandstones Y1 and Y2, the wave velocity anisotropy parameters ε, γ, and ζ change exponentially or quadratically with increasing confining pressure, and Y2 has a greater correlation coefficient of anisotropy parameters than Y1, but there is no wave velocity anisotropy in Y3. In addition, in dry, water- and oil-saturated conditions the relationships between ε,γ and p or γ, ζ and p are quite distinct from each other, that is, the anisotropy factors ε, γ and ζ of Y1 and Y2 exhibit a clear correlation with pressure and the fluid property, and the ε and γ in oil-saturated condition are larger than that in the corresponding water-saturated condition at the experimental pressure. The experimental results can provide an important basis for the interpretation of seismic data, identifying oil and water zone and comparing with well log data in that region.