基于超声测试的页岩岩石物理特征分析

Analysis of physical characteristics of shale rock based on ultrasonic testing

针对中国东北通化地区页岩层理的发育特点,根据两个方向的三轴压缩实验和纵、横波速度测试,分析了页岩弹性模量、泊松比和纵横波速度在不同方向的变化规律。实验数据分析表明:不同围压条件下页岩各向异性参数ε与γ间存在线性相关性,应用线性回归建立的经验公式可为二者相互预测或测试提供参考;有利储层岩样的各向异性程度明显大于不利储层;随着围压的增高,纵、横波速度均增大,ε和γ均减小;页岩的纵横波速度比与密度呈正相关,因而与总有机碳含量(TOC)呈负相关,高TOC有利储层的纵横波速度比明显小于1.7,而低TOC的非有利储层纵横波速度比均高于该值,可作为区分不利储层的标志;平行于层理方向的页岩弹性模量随着孔隙度的增高而变大,垂直于层理方向的弹性模量随着孔隙度的增高而减小,可为页岩脆性和甜点地震定量预测提供依据。

Given the development of shale bedding in Tonghua,Northeast China,tri-axial compression experiments and P&S wave velocity(vPand vS)tests in two directions are carried out to analyze the variation of elastic modulus,Poisson’s ratio,vP,and vSof shale in different directions.Relevant experiment data show that the shale anisotropy parametersεandγare linearly correlated under different confining pressure and the empirical formula built by linear regression can provide references for their prediction or testing.The anisotropy of favorable reservoir samples is much higher than that of unfavorable ones.As the confining pressure gets higher,both vPand vSincrease andεandγbecome smaller.The vP/vSof shale is positively correlated to density and therefore negatively to total organic carbon (TOC).The vP/vSof favorable reservoirs with high TOC is much lower than 1.7,while the ratio of unfavorable reservoirs with low TOC is higher than this value,which can be taken as a marker to distinguish unfavorable reservoirs.With the increase in porosity,the elastic modulus of shale parallel to the bedding direction rises but declines vertical to the bedding direction.Our findings can lay a foundation for the seismic quantitative prediction of shale brittleness and sweet spots.