套管井中偏心对声场的影响分析

Effects of the eccentralization on acoustic wave propagation in cased boreholes

目前在油田的实际应用中,声幅-变密度水泥胶结测井(CBL/VDL)在套管井的水泥胶结质量评价中发挥重要作用。但是,在一些大斜度井或者水平井中,往往由于仪器或者套管的重量等原因导致套管井中出现偏心现象,这给利用声波测井资料进行水泥胶结质量评价带来一些难题。为此,本文建立了套管偏心和仪器偏心两种情况下的三维声学模型,利用柱坐标系下的三维交错网格有限差分算法数值模拟了两种偏心情况下的声波传播情况,并着重研究了偏心率的变化对套管井中声场波形特征,尤其是套管波及地层波特征的影响。另外,模拟了具有不同外径尺寸的套管和偏心率的组合情况下的声场传播情况,在此基础上研究了偏心率的大小对声场特征的影响规律。本文的研究结果表明,套管偏心和仪器偏心均会给声场波形特征带来影响,且随着偏心率的增加而增大;相比较而言,仪器偏心对套管波的影响更大。

In practice, cement bonding log-variable density log （CBL/VDL） plays an important role in the evaluation of cement bonding conditions in cased boreholes. However, in highly deviated wells or horizontal wells, eccentralization often occurs caused by the weight of tools and casing or other factors, resulting in challenges in the evaluation of bonding conditions using acoustic logging data. Therefore, 3-Dimentional acoustic models for two kinds of eccentralization were established in the paper, and the propagation of acoustic waves in such models was numerically studied. Then, the impact of eccentricity on the characteristic of casing wave and formation wave were analyzed in detail. Specially, wave propagation in cased boreholes with different casing diameters and eccentricity were also investigated, the variations of the amplitude of casing wave and formation wave with different parameters were studied. The results indicate that eccentralization from both the casing and tools can influence the features of waveforms gathered in the borehole, and the effects increase with the increase of eccentricity. Moreover, eccentralization of tools have stronger impact on casing wave than that of casing.