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在进行 VSP 测量时,为了减少电缆波、保证激发的重复性,我们采用电火花震源在井中潜水面以下5米处以不同的能量激发,井下检波器要保持和井壁紧密接触,深度间隔为20—50米之间,电缆要处于松弛状态。资料处理的关键在于根据地震测井资料建立的速度模型,求出校正量。然后利用 VSP 测量的各道时间减去其对应的校正量,得到一条类似于地面地震观测中的自激自收时间剖面。最后通过二维滤波处理,消除了低视速度的电缆波和套管波。应用 VSP 资料可以测定地震波频率随深度变化的曲线,进而求得吸收系数,它还可用于烃类检测,了解井孔附近的地质构造和岩性特征。
In the VSP measurement, in order to reduce the cable wave, to ensure the repeatability of excitation, we use a spark source 5 meters below the surface of the well with different excitation energy, downhole geophone and the well wall to maintain close contact with the depth interval of 20 -50 meters, the cable should be in a relaxed state. The key to data processing is to find the correction amount based on the velocity model established by seismic logging data. And then use the VSP measurement of each time minus the corresponding correction, get a similar to the ground-based seismic observation in the self-excitation time of self-absorption profile. Finally, through the two-dimensional filter processing, eliminating the low-speed cable wave and casing wave. VSP data can be used to determine the curve of seismic wave frequency with depth, and then to obtain the absorption coefficient. It can also be used for hydrocarbon detection to understand the geological structure and lithology characteristics near the borehole.