裂隙密度对纵波传播特性影响的实验观测

Experimentally surveying influence of fractural density on P-wave propagating characters

在利用纵波对裂隙储层预测中,速度和振幅是两个不可缺少的参数,实际资料处理时更需要知道裂隙密度与速度和振幅的关系。在实验室,通过把圆薄币状填充物嵌入基质材料中的方式来模拟裂隙模型,制作了裂隙密度从0到12%的9种裂隙模型,并用四种频率的超声纵波换能器测试了平行和垂直裂隙方向上的纵波速度和透射振幅,得到了裂隙密度与纵波速度及振幅曲线。实验表明,纵波沿裂隙方向传播时,其速度随裂隙密度变化的影响不大,当裂隙密度增大到12%时,速度仅有2%的变化;纵波垂直裂隙传播时,速度比平行传播时下降一半。随着裂隙密度的增加,纵波振幅下降的趋势不但与裂隙密度有关也与频率相关。实验结果定量地给出了在裂隙介质中裂隙密度和频率对纵波参数的影响。

The velocity and amplitude are necessary parameters when using P-wave to predict the fractur-al reservoir and it is necessary to know the relationship between the fractural density and velocity/amplitude in practical data processing. In lab, the fractural model is simulated by embedding the circle and thin coin into base material, fabricating 9 fractural model with fractural densities from 0 % to 12%; and using ultrasonic transducer with 4 frequencies to test P-wave velocity and transmission energy in the directions parallel and vertical to fracture. getting the curves of fractural density vs P-wave velocity and amplitude. The experiments showed when P-wave propagates along the fractural direction, the variation of fractural density has little influence on velocity: only 2% variation of velocity when the fractural density is increased by 12%; when P-wave propagates vertical to fracture ,the velocity is decreased by half in comparison with parallel to fracture. Along with the increase of fractural density, the decreasing tendency of P-wave amplitude is relative not only to fractural density, but also to frequency. The experimental results quantitatively gave the influence of fractural density and frequency on P-wave parameters in fractural medium.