层理对页岩纵波特性的影响

Influence of bedding on compressional wave characteristics of shales

研究层理性页岩声波响应特征有助于利用声波测井资料指导页岩气井安全钻井。采集四川盆地长宁地区下志留统龙马溪组露头页岩岩样,并沿不同角度钻取页岩岩心。基于多频声波测试系统,开展了多层理角度下页岩声波实验,分析了层理角度对纵波速度、衰减系数、时域、频域等特性的影响。开展了数值模拟实验,分析了岩心端面垂直时平行层理面、层理密度对波速、衰减的影响。结果表明:随着层理角度增大声波时差、声波衰减系数均线性增大;声波速度存在频散现象,测试频率不同,声波速度不同;声波速度与层理密度呈线性负相关;层理角度对页岩声波主频没有影响。该研究结果为页岩气井安全钻井及压裂改造等工程设计提供了参考。

Studying the acoustic characteristics of layered shales contributes to applying acoustic logging to guide drilling safely.The shale samples were collected from the Lower Silurian Longmaxi Formation in Changning area of Sichuan Basin,and drilled into cores along different orientation relative to the bedding plane.Based on multi-frequency ultrasonic wave testing system,acoustic wave experiments of shale samples were carried out and the influences of bedding angle on acoustic wave velocity,attenuation coefficient,time domain and frequency domain were analyzed.Numerical simulation experiments were carried out to analyze the influences of bedding density on wave velocity and attenuation in parallel and vertical core end faces.The results show that the interval transit time and the attenuation coefficient increase linearly with the increase of bedding angle.Frequency dispersion phenomenon exists,which shows that the acoustic velocity varies with the testing frequency.Acoustic velocity is negatively correlated with bedding density,and bedding angle has no effect on the dominant frequency of shale acoustic waves.The results provide a reference for the drilling and fracturing engineering of shale gas wells.