固井第一界面微环隙对声波传播规律的影响

Effect of Microannulus on Sonic Wave Propagation at First Cementing Interface

为消除微环隙对固井质量评价的影响,研究微环隙对声波传播的影响规律是非常必要的。针对微环隙对声波传播的影响,分别进行了实验室试验和理论计算。试验采用简化的平板模型,用中间挖空填水的超薄塑料薄膜来模拟充水微环隙。根据试验模型的特点,由声波在多层介质平面层的透射理论得到微环隙影响声波传播的理论计算公式。试验结果表明,声波首波幅度随微环隙尺寸的增大而减小,当微环隙尺寸增大至0.1mm时声波透射幅度减小70%左右,这会造成测井时接收到的反射波声幅的增大,可能将固井质量合格的井解释为不合格。理论计算印证了试验结果,同时也说明声波传播对充气微环隙的敏感程度高于充水微环隙。研究得出,微环隙对声波传播的影响是非常显著的,在声波测井中其影响规律可以应用于对固井质量的评价中。

To eliminate the effect of microannulus on cementing quality evaluation ,it is necessary to investi-gate the effect of microannulus on sonic wave propagation .Experimental study and theoretical analysis were used to conduct this research .Adopting a simplified plate model ,the microannulus was simulated by thin plastic film filled with water .According to the characteristics of the experimental model ,the calculation formula that microannulus effects sonic wave was obtained by using the theory of sonic wave transmission in multi-medium plane layer .Exper-imental results showed that first sonic amplitude decreases with the increase of microannulus size ,when microannu-lus size is increased to 0.1 mm ,the sonic wave amplitude will be decreased by 70% .This will lead to an increase of received amplitude in logging and cause incorrect cementing explanation and evaluation .Both theoretical calculations and experimental study showed that sensitivity of sonic wave propagation in microannulus with air is higher than that filled with water ,the effect of microannulus size on sonic wave propagation is very significant ,its regularity could be used to evaluate the cementing quality by sonic logging .