不同影响因素下致密灰岩声波特性研究

Acoustic Characteristics Research of Dense Limestone under Different Influencing Factors

在研究岩石力学性质、获取地层参数的过程中,岩石的声波特性发挥着重要作用。为了研究致密灰岩的声波特性,从鄂尔多斯盆地3 500 m以下4段灰岩地层取不同孔隙度的岩样进行实验,研究了不同孔隙度、层理、围压、轴压对致密砂岩声波性质的影响。实验结果表明,3 500 m以下致密灰岩的孔隙度分布在5%-13%之间,并且随着孔隙度的增加,灰岩的弹性模量减小,纵横波速呈线性减小;致密灰岩在平行层理方向纵横波速大于垂直层理方向,因为垂直层理方向灰岩声阻抗大;在0-5 MPa内,随着围压增大致密砂岩纵横波速增大明显,围压继续增大,纵横波速变化不明显;轴压较小时,致密灰岩的纵横波速随着轴压的增大变化不明显,当轴压增大到一定程度时,不同围压下纵横波速基本一样,围压对其影响减小。

During the process of doing research of rock mechanical properties and obtaining the formation parameters,the acoustic characteristics of rock play an important role. To do research of the acoustic characteristics of dense limestone,experiments of limestone with different porosity which are exploited under 3 500 m from 4 piece of limetone strata in Ordos Basin are done and the impacts of porosity,bedding,confining pressure and axial pressure on the acousic characteristics are studied. The results show that,the porosity of dense limestone under 3 500 m distributes from 5% to 13%,and the elasticity modulus decreases with the porosity increasing; the vertical and horizontal wave velocity decresaes linearly with the increase of porosity and the decrease of elasticity modulus; the vertical and horizontal wave velocity along parallel bedding is bigger than that along vertial bedding due to the bigger acoustic impedance; Within the（ 0 - 5） MPa,the vertical and horizontal wave velocity increase greatly with the increase of confining pressure,while them nearly keep the same when the confining pressure is higher than 5 MPa. When the axial compression is low,the vertical and horizontal wave velocity almost change nothing with the increasing of the axial pressure; while the axial compression is high enough,the vertical and horizontal wave velocity have the same value under different confining pressure and the effect of confining pressure is small.