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常规声波测井解释方法建立在各向同性地层中的垂直井基础之上,对各向异性地层中的水平井和斜度井并不适用。在水平井和斜度井的钻井过程中,岩屑会溅到井壁并最终在井壁底部形成一层薄岩屑层。同时,高速层和各向异性也可能会影响声波时差的测量。本文采用结合了Hybrid-PML的交错网格时域有限差分方法(SGS-FDTD),研究阵列声波仪器在各向异性介质中的水平井和斜度井条件下,不同因素对测得时差所带来的影响。模拟结果揭示了声波时差在高速层,薄岩屑层,井斜角,层厚,各向异性等不同影响因素下的相应规律。我们发现当波长远小于井壁与高速层的距离时,能够准确测得目的层时差;然而在两者处于同一量级时的近场条件下,几何声学理论不再适用;当井眼底部存在岩屑层时,费马原理依旧适用,对真实时差测量没有影响;在各向异性地层环境下,井斜角的增大使得测得时差由垂直向时差逐渐趋近于水平向时差;对于特定源距的声系,仪器在目的层中所移动的距离超过一定距离时,方可获得薄层时差值。基于不同井斜角和不同各向异性大小均匀TI地层模型的模拟结果,绘制了时差估计图版,可以对任意井斜角和各向异性比的模型进行时差的定量估计。通过对不同声系和不同弹性参数的模拟实验,证明了这种时差估计方法对TI地层中的水平井和斜度井准确有效。
Conventional acoustic logging interpretation methods are based on vertical wells in isotropic formations and are not suitable for horizontal and inclined wells in anisotropic formations. During drilling of both horizontal and inclined wells, debris will splash over the borehole wall and eventually form a thin layer of lithic debris at the bottom of the borehole wall. At the same time, high-speed layers and anisotropy may also affect the measurement of acoustic time differences. In this paper, staggered-grid finite-difference time-domain method (SGS-FDTD) based on Hybrid-PML is used to study the influence of different factors on the measured horizontal and vertical wells of an anisotropic medium The impact of coming. The simulation results reveal the corresponding laws of acoustic time lag under different influencing factors such as high-velocity layer, thin-clastic layer, well inclination angle, layer thickness and anisotropy. We find that when the wavelength is far less than the distance between the well wall and the high-velocity layer, the target layer time difference can be accurately measured. However, when the two are in the same order of magnitude, the geometrical acoustic theory is no longer applicable. When the bottom of the well exists In the case of cuttings, the Fermat principle is still applicable and has no effect on the real time difference measurement; in the anisotropic formation environment, the increase of the inclination of the well causes the measured time difference to gradually approach the horizontal difference from the vertical to the time difference; Acoustic system from the source, the instrument in the target layer to move more than a certain distance away from when the layer can be obtained when the lag value. Based on the simulation results of TI model with different well inclination and anisotropy, the time-difference plot is plotted, which can make a quantitative estimation of the time difference of the model with arbitrary well angle and anisotropy ratio. The simulation experiment of different acoustic systems and different elastic parameters proves that this method of time difference estimation is accurate and effective for horizontal wells and inclined wells in TI strata.