Wavefield simulation and analysis with the finite-element method for acoustic logging while drilling in horizontal and deviated wells
Wavefield simulation and analysis with the finite-element method for acoustic logging while drilling in horizontal and deviated wells
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DOI：
10.1190/geo2012-0542.1
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发表时间：
2013-10
期刊：
影响因子：
3.3
通讯作者：
Hua Wang;G. Tao;Kuo Zhang
中科院分区：
文献类型：
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作者：
Hua Wang;G. Tao;Kuo Zhang
为了有效地研究水平井和大斜度井声多极随钻测井(LWD)仪器产生的波场，提出了一种结合复频移完全匹配层(CFS-PML)边界的频域有限元方法。利用这种有限元方法，可以很容易地在仿真中对称地设置源和接收器，从而准确地模拟真实的刀具，而这在有限差分法中是很难处理的。此外，该算法能够更有效地实现CFS-PML边界。我们应用这种方法来研究工具偏心对慢速地层测量的影响，这些地层最可能需要水平井和大斜度井中随钻测井的3D解。我们发现，由于仪器不能集中在这些井中，在单极子测量中可能出现一些非单极子模式，在偶极子测量中可能出现Stoneley模式；弯曲环波可能随着工具偏心率的增加而变得越来越强，Stoneley模式可能是较晚到达的事件，特别是在严重偏心的四极仪器的情况下。在此基础上，提出了一种利用偏心偶极子测量中的相位差来量化工具偏心程度和偏心角度的方法，这些参数对于分析地质导向中的井底组件性能非常有用。
We developed a frequency-domain finite-element method (FFEM) in conjunction with a complex-frequency-shifted perfectly matched layer (CFS-PML) boundary to effectively study the wavefield generated by acoustic multipole logging-while-drilling (LWD) tools in horizontal and highly deviated wells. With such an FFEM, the sources and receivers can be easily set symmetrically in the simulation to model the real tools exactly, while this is very difficult to deal with in the finite-difference method. In addition, the CFS-PML boundaries can be implemented more efficiently in this algorithm. We applied this method to study the effects of tool eccentricity on the measurements in slow formations that most likely need 3D solutions for LWD in horizontal and highly deviated wells. We found that because the tool cannot be centralized in these wells, some nonmonopole modes could appear in monopole measurements and the Stoneley mode could appear in dipole measurements; the flexural collar wave could become increasingly strong with an increase of tool eccentricity, and the Stoneley mode may be the later arriving event, especially in the case of a severely eccentric quadrupole tool. Based on these studies, we introduced a method to quantify the extent and the angle of the tool eccentricity with the phase difference in eccentric dipole measurements.These parameters areveryuseful forthe analysis of the bottom-hole assembly performance in geosteering.