第一界面流体环厚度对套管首波的影响

The effects of the fluid annulus thickness at the first interface on the casing wave

基于简化的套管井模型,数值计算了第一界面胶结状况不同时的井内声场,考察了第一界面处流体环厚度变化时井内声场二维谱、激发谱及时域波形的变化特征。数值和分析结果表明:二维谱可以比较清楚地显示各波型成分的变化规律;第一界面未胶结而第二界面胶结良好时,波列首波是套管波,它是一种速度略低于钢套管纵波速度的导波;此时,即使套管与水泥环之间存在间隙非常小的微环,套管波的能量也会急剧变大;套管波幅度会随流体环厚度的增大而增大,但当流体环厚度大到一定值时(如8mm),其增大趋势稍变平缓。

Based on the simplified model of cased borehole,acoustic wave field in the borehole is numerically calculated when the bonding conditions of the first interface are different.The variation features of the two-dimension spectrum,excited spectrum and the waveform in time domain of acoustic wave field in borehole are investigated as the thickness of the fluid annulus at the first interface is varied.The numerical results show that two-dimension spectrum could re-veal the changing law of each wave composition clearly.When the first interface is not boned while the second interface is well boned,the head wave is the casing wave,which is a guided wave traveling at a speed lower than the compres-sional wave in steel casing.Meanwhile,even there is a very tiny micro annulus between casing and cement annulus,the energy of casing wave will also increase sharply.The amplitude of the casing wave will increase with the increase of the thickness of the fluid annulus,however,when the thickness of the fluid annulus increases to a fixed value（such as 8mm）,the increasing trend will be smooth.