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采用地震波的双源传递机理和正压介质模型 ,可以对疏松地质介质中点爆炸震源产生的干扰波进行理论研究。本文提出 ,在疏松激发层中易于产生低频稀疏纵波和低频 SV面波干扰 ,并给出了相应的解析近似解。结果表明 ,对给定的激发层厚度、岩性、有效信号低端频率和波的时域衰减陡度 ,存在一个最小井深 Hmin。当炮孔深度大于 Hmin时 ,增大井深可以更好地压制干扰。如果炮孔深度小于 Hmin,增大井深并不能削弱稀疏纵波 ,反而使这一干扰波更强。当 Hmin大于激发层厚度时 ,则井深增大同样使稀疏纵波干扰更强。结果还表明 ,存在一个由岩性和波的时域衰减陡度决定的临界井深增量Δ H ,当井深增量远小于这一值时 ,井深增量变化并不能显著削弱 SV面波干扰。文中研究结果较好地解释了在井深试验时常常碰到的似是而非的现象。对于提高野外资料采集质量和在处理中压制干扰波提供了一个理论模型近似。
Using the dual-source transmission mechanism of seismic waves and the model of positive pressure medium, the interference waves generated by the mid-point explosion in the loose geological medium can be theoretically studied. In this paper, it is proposed that the low-frequency sparse longitudinal and low-frequency SV surface-wave interferences tend to be generated in the loose excitation layer, and corresponding analytic approximate solutions are given. The results show that there is a minimum well depth Hmin for a given excitation layer thickness, lithology, low frequency of the effective signal and steepness of the time-domain attenuation of the wave. When the borehole depth is greater than Hmin, increasing the depth of the well can suppress the interference better. If the borehole depth is less than Hmin, increasing the depth of the well does not weaken the sparse P-wave, but instead makes the spurious wave stronger. When Hmin is greater than the thickness of the excitation layer, then the increase in well depth also makes the sparse longitudinal wave interfere more strongly. The results also show that there is a critical well depth increment, Δ H, determined by lithology and wave steepness of the time domain decay. When the well depth increment is much smaller than this value, the increment of well depth does not significantly impair SV surface wave interference. The results in this paper better explain the paradoxical phenomenon often encountered in well testing. It provides a theoretical model approximation for improving the quality of field data acquisition and suppression of interference waves in processing.