利用一维单道声反射实现强声阻抗介质下的流体层厚度反演方法

Thickness Reversion Method of Water Layer Behind High Acoustic Impedance from One dimension Reflective Data

针对单道超声反射式水泥胶结测井 ,从理论方法上研究如何从一维反射资料反演第一界面窜槽时水层的厚度 .通过选择套管共振透射窗 ,提高目的层有用信号的信噪比 .内层介质 (水和水泥 )厚度出现在声波相应介质层的相移φ(ω) =nπ+φ0 (ω)中 ,利用多个频率点的相移反正切函数主值给出相应的 n值计算公式 ,并把 n值的整型性作为反演收敛的判据之一 .在已知条件下 ,采用牛顿迭代法对人工合成单道反射波信号反演了窜槽水层厚度 ,在模拟实际窜槽水层厚度为 1 mm和 3mm情况下 ,均得到满意的结果 ,而且反演结果的精度对初值的选择不敏感 。

Thickness reversion method of water layer from one dimension reflective data in ultrasonic reflective cement bond logging is theoretically studied when the first interface is bad bonded. The signal to noise of the useful signal of objective layers is greatly improved by reflective coefficients in the window of resonance and transmission. The thickness of inner medium (water and cement) appears phase shift φ(ω)=nπ+φ 0(ω) . The formula of n is obtained with the main value of the arctangent functions of phase shift. The quality of the integer of n is expressed as the reversion criterion of convergence. Under the excepted thickness of water layer and cement layer, all the parameters are known, the thickness reversion of water layer is made with one path synthetic reflective signal by means of Newton iteration method. When the thickness of water layer is several millimeters, satisfied results are obtained. The precision of the inversion result is not sensitive to the selection of initial value so that the feasibility of the reversion method is proved preliminarily.