Mapping formation shear-velocity variation by inverting logging-while-drilling quadrupole-wave dispersion data
Mapping formation shear-velocity variation by inverting logging-while-drilling quadrupole-wave dispersion data
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DOI：
10.1190/geo2013-0136.1
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发表时间：
2013-11-01
期刊：
影响因子：
3.3
通讯作者：
Zhao, Long
中科院分区：
文献类型：
--
作者：
Su, Yuan-Da;Tang, Xiao-Ming;Zhao, Long
随钻测井四极子波是由钻铤沿井眼沿着传播的一种色散波。该波对钻井引起的地层变化很敏感。我们反演LWD四极波频散数据，以估计远离井筒的径向剪切速度剖面。我们还探讨了非唯一性的反问题，并解决了它，通过使用约束反演方法。这是通过使用近井速度计算的另一条曲线来约束模型频散曲线的高频部分来完成的。该约束条件是基于高频随钻四极子波穿透深度较浅，对近井剪切速度敏感的物理原理。特别是，我们发现，一个单调连续的速度剖面可以很好地近似使用一个区域的等效模型，允许急剧简化的反演过程。利用理论建模和真实的资料实例对该方法进行了验证。四极色散数据和反演结果清楚地表明，即使在钻井过程中也会发生地层蚀变。
The logging-while-drilling (LWD) quadrupole wave is a dispersive wave mode guided along the borehole with a drill collar. The wave is sensitive to the formation alteration caused by drilling. We inverted LWD quadrupole-wave dispersion data to estimate a radial shear-velocity profile away from the wellbore. We also explored the nonuniqueness of the inverse problem and solved it by using a constrained inversion method. This was done by constraining the high-frequency portion of the model dispersion curve with another curve calculated using the near-borehole velocity. The constraint condition is based on the physical principle that a high-frequency LWD quadrupole wave has a shallow penetration depth and is therefore sensitive to the near-borehole shear velocity. Particularly, we found that a monotonically continuous velocity profile can be well approximated using a one-zone equivalent model, allowing for a drastic simplification of the inversion process. We used theoretical modeling and real data examples to validate the method for the LWD wave data. The quadrupole dispersion data and the inversion results clearly demonstrated that formation alteration can occur even while the well is being drilled.