Frequency-domain simulation of logging-while-drilling borehole sonic waveforms
Frequency-domain simulation of logging-while-drilling borehole sonic waveforms
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DOI：
10.1190/geo2013-0279.1
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发表时间：
2014-02
期刊：
影响因子：
3.3
通讯作者：
P. Matuszyk;C. Torres‐Verdín
中科院分区：
文献类型：
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作者：
P. Matuszyk;C. Torres‐Verdín
随钻声波测井（LWD）井眼测量的数值模拟具有挑战性，因为由于巨大的钻铤占据了井眼的很大一部分，因此会产生明显的波传播效应。此外，随钻工具的内部结构会对测量到的斯通利模式和四极模式的色散产生重大影响。接箍通常由一组内部周期凹槽构成，这些凹槽充当机械过滤器，以衰减不希望的接箍模式。对随钻测井声波波形进行可靠的数值模拟和解释，需要将钻铤的所有特征和尺寸都包含在模拟模型中。此外，由于通常用于截断计算域的完全匹配层（PML）中的反向传播模式，钻铤的存在会导致数值不稳定。当模拟仅仅是为了再现周围岩层中的波传播时，可以通过在接箍中实施人工粘弹性衰减来规避这个问题。此外，在材料特性和LWD接箍内部结构存在较大差异的情况下，要对井眼波传播进行可靠的建模，需要一种能够准确、稳定地解析模型中所有光谱尺度的数值方法。我们在频域采用了一种自动自适应有限元方法，结合PML技术来模拟LWD声波测井测量。应用实例验证了在LWD接箍中存在套管和内部结构的情况下，模拟井眼和地层传播模式的准确性和可靠性。钢套管的存在和套管/地层胶结的质量对井内激发的传播模式有显著影响。然而，在快速地层中，无论水泥胶结质量如何，使用单极子和四极子源仍然可以估计地层剪切慢度。强管道模式严重阻碍了地层压缩慢度的评估。在低速地层中，由于套管和强环空模式的存在，当套管胶结质量较差时，估计地层剪切慢度实际上是不可能的。
Numerical simulation of sonic logging-while-drilling (LWD) borehole measurements is challenging because of significant wave propagation effects due to the massive drilling collar occupying a large portion of the borehole. In addition, the internal structure of the LWD tool can have a significant impact on the measured dispersions of Stoneley and quadrupole modes. The collar is typically constructed with a set of inner periodic grooves, which act as a mechanical filter to attenuate undesirable collar modes. Reliable numerical simulation and interpretation of LWD sonic waveforms requires that all features and dimensions of the drilling collar be included in the simulation model. Furthermore, the presence of the drilling collar can prompt numerical instabilities due to backward propagating modes in the perfectly matched layer (PML) commonly used to truncate the computational domain. This problem can be circumvented with the implementation of artificial viscoelastic attenuation in the collar whenever the simulations are intended to reproduce only wave propagation within the surrounding rock formations. In addition, reliable modeling of borehole wave propagation in the presence of high contrasts in material properties and the internal structure of the LWD collar requires a numerical method capable of accurately and stably resolving all spectral scales present in the model. We implemented an automatic hp-adaptive finite-element method in the frequency domain combined with a PML technique to simulate LWD sonic logging measurements. Examples of the application verified the accuracy and reliability of the simulated borehole and formation propagation modes in the presence of casing and internal structures in the LWD collar. The presence of steel casing and quality of casing/formation bond significantly influence the propagation modes excited in a borehole. However, it is still possible to estimate the formation shear slowness using monopole and quadrupole sources regardless of the quality of cement bond in fast formations. Assessment of the formation compressional slowness was significantly impeded by the strong pipe mode. Estimation of formation shear slowness in slow formations is practically impossible due to the presence of casing and a strong annulus mode when the quality of casing bond is poor.