The radial heterogeneity of near-wellbore formation is frequently encountered in petroleum exploration and production. It usually manifests as the variations of formation wave velocities in radial position. Mapping radial variations of formation velocities is of great significance in identifying invaded zones and determining rock properties, which are valuable for engineering measures, such as fracturing, wellbore stability evaluation and optimal well completion. A stepwise inversion scheme is developed to image the radial profiles of formation P- and S-wave velocities. Instead of determining the formation velocity variation and its corresponding radial position simultaneously as traditional methods do, the inversion procedure is divided into two steps: the velocity array is determined by semblance processing of contiguous receiver pairs of acoustic array data, and then the thickness of the layer (radial position) is obtained based on ray theory. The inversion results from Step 1 could be used to guide the operation and decide whether Step 2 is necessary. In addition, calculation on the arrival time of waves is not required in this inversion method, thus mitigating the inaccuracy in processing field data with noises. Firstly, the wave field characteristics of heterogeneous formation models have been analysed, indicating that both amplitude and arrival time differences are caused by heterogeneity. The waveforms are then processed using the stepwise inversion method to estimate the radial profiles of formation wave velocities, where the factors influencing the inversion procedure are also studied. It is shown that, longer TR spacing is required for a specific investigation depth with the decreasing of velocity ratio; the resolution of the velocity inversion profile degrades with the increasing number of receiver pairs. The modelling-based inversion results and the application to field data indicate that, in addition to profiling formation P-wave velocity, our proposed methodology also has encouraging application in mapping formation S-wave velocity. The efficiency and accuracy of the stepwise inversion method enables real-time implementation with fast calculation speed, thus providing useful information of monopole acoustic well logging for engineering.

在石油勘探和生产中经常遇到近井眼形成的径向非均质性。它通常表现为径向位置中地层波速度的变化。绘制地层速度的径向变化图对于识别侵入带和确定岩石性质具有重要意义，这对于工程措施（例如压裂，井眼稳定性评估和最佳完井）具有重要意义。开发了逐步反演方案以成像地层P和S波速度的径向剖面。代替传统方法同时确定地层速度变化及其对应的径向位置，反演过程分为两个步骤：通过对声阵列数据的相邻接收器对进行似然处理来确定速度阵列，然后基于射线理论获得层的厚度（径向位置）。步骤1的反演结果可用于指导操作并确定步骤2是否必要。另外，在该反演方法中不需要计算波的到达时间，从而减轻了在处理带有噪声的场数据时的不准确性。首先，分析了非均质地层模型的波场特征，表明振幅和到达时间的差异都是非均质性引起的。然后使用逐步反演方法对波形进行处理，以估算地层波速的径向分布，并在其中研究影响反演程序的因素。结果表明，随着速度比的减小，特定的探测深度需要更长的TR间距。速度反转曲线的分辨率随着接收器对数量的增加而降低。基于建模的反演结果和在野外数据中的应用表明，除了分析地层纵波速度外，我们提出的方法在映射地层横波速度方面也具有令人鼓舞的应用。逐步反演方法的效率和准确性使得实时实现具有快速的计算速度，从而为工程提供了单极声波测井的有用信息。速度反转曲线的分辨率随着接收器对数量的增加而降低。基于建模的反演结果和在野外数据中的应用表明，除了分析地层纵波速度外，我们提出的方法在映射地层横波速度方面也具有令人鼓舞的应用。逐步反演方法的效率和准确性可实现快速计算的实时实现，从而为工程提供单极声波测井的有用信息。速度反转曲线的分辨率随接收器对数量的增加而降低。基于建模的反演结果和在野外数据中的应用表明，除了分析地层纵波速度外，我们提出的方法在映射地层横波速度方面也具有令人鼓舞的应用。逐步反演方法的效率和准确性使得实时实现具有快速的计算速度，从而为工程提供了单极声波测井的有用信息。