含煤层地质环境下地震波场的数值模拟

NUMERICAL SIMULATION OF SEISMIC WAVE-FIELDS UNDER THE GEOLOGICAL BACKGROUND OF COAL SEAM

本文对含低速煤层地质环境下弹性波场多波多分量地震资料进行厂二维数值模拟研究，对人工边界反射进行了有效处理，频散效应得到了有效的压制，对几种不同激发与观测排列方式下（地面激发、低速煤层中激发以及地面观测与VSP观测）的弹性波资料进行了模型计算与分析．结果表明：低速煤层中激发时，由于煤层上下项底板介质的高速特性，其反射极性相反，在VSP地震记录上会出现煤层段记录到的波场相长干涉现象．振幅放大；地面地震记录上会出现”亮点”现象．地面激发时，地震记录上会出现“暗点”现象．而且，VSP与地面记录上，低速层中干涉后的波场与反射彼场波形展党，且存在频散效应，这些特征可能是低速煤层在地面或VSP观测地震记录上的重要指示信息，值得进一步研究与应用．

This paper presents a study of numerical simulation for the elastic wave-fields of multi-wave and multi-component scismic records under the geological background of coal seam. Both the artiflcial boundary reflection and the grid dispersion, which produces in the Fmite-difference calculations, is effectively treated in this paper. The seismic records,which are obtained under different conditions of excited sources (at the free surface and in the lower velocity layer) and observcd methods (at the free surface and in wcll), are simulated and analyzcd. When thc sourcc is placcd in the lower vel0city laycr, both the interference of the phasc-length of selsmic waves and widen amplitudes can be seen from the VSP. records, and the 'lighting spot' phenomenon can be also seen from the surface records. It is because there are the characteristics of high velocities in top layer and bottom layer media and the polarities of reflection waves are contrary. When the excited source is placed at the free surface, the 'darking spot' phcnomcnon can be found from the seismic records. Meanwhile, the wave-form expansion of seismic wave-field and reflection wave-field in the lower velocity layer is shown in VSP records and surface records because these waves interfcre with cach other, and there is dispersion in the lower velocity layer.Perhaps these charactcristics are some important information which the lower velocity layer presents in these surface records and VSP records. It is worth further research and application.