井下震源和阵列震源的远场辐射花样

Far-field radiation pattern of downhole source and array source

本文详细研究了充流体井中由不同类型轴对称震源激发的弹性波低频远场辐射花样。轴对称源包括:①井轴上的点膨胀源和点膨胀阵列源;②井壁上的径向应力源和径向应力阵列源:③井壁上的切向应力源和切向应力阵列源。文中对使用的源频率范围进行了讨论.并对不同类型震源激发的纵波和横波的辐射花样作了数值计算。研究结果表明;低频远场近似的方法可适用于井眼半径为10cm,源频率低于700Hz的井下震源;井轴上的点膨胀源和井壁上的径向应力源在井内激发管波,在地层中激发纵波和横波;而井壁上的切向应力源在井内不激发管波.仅在地层中激发纵波和橫波;阵列震源能使辐射强度大大提高。

We detail the far-field radiation patterns of low-frequency elastic waves generated by different axially symmetric sources in fluid filled borehole. Axially-symmet-ric sources are point volume source and point volume array source which are aligned along borehole axis,the radial stress source and radial stress array source which are distributed on borehole wall, and the tangential stress and tangential stress array sources which are on borehole wall. Source frequency ranges are discussed.and radiation patterns of P and S-waves generated by different kinds of sources are estimated numerically. The research result says that low-frequency far-field approximation is applicable to the downhole source which has frequency below 700Hz and is placed in a borehole 10cm in diameter. Both the point volume source on borehole axis and the radial stress source on borehole wall produce tube wave in borehole.but P and S-waves in formations. The tangential stress source on borehole wall only causes P and S-waves in formations. Array sources enhance radiation greatly.