准噶尔南缘山前二维多波勘探近地表影响因素分析

Influence of near surface structure on multi-wave exploration at the mountain front of South Junggar Basin

准噶尔盆地近地表对地震资料有显著的影响。在南缘四棵树凹陷高泉背斜部署的一条三分量采集的二维测线的对比中发现,转换横波剖面相比纵波剖面在测线的东段信噪比和能量明显降低。为了进一步分析验证近地表对多波多分量资料的影响,以实际的近地表模型和井资料建立正演模型,按照实际的观测系统进行了单炮的正演,通过对剖面和单炮的分析结合近地表结构调查,发现在东段由于奎屯河的冲刷沉积,低降速带厚度明显加厚,西域砾岩发育,这是造成多波资料能量、信噪比降低的主要因素,而且转换横波相比纵波更易受近地表吸收衰减的影响。

In Junggar basin,near surface structure is an obvious factor influencing seismic data.2D 3C seismic line data were collected recently at Gaoquan anticline of the mountain front area.Nevertheless,S/N of PS-wave section was obviously lower than P-wave section at the east end of 2D line.To verify and analyze near surface structure's influence on multi-wave 3C seismic data,the authors built forward model by using its near surface structure and well-logging data so as to get modeling shots with real acquisition geometry.By analysis of modeling results and near surface structure investigation,it is found that the thickness of low velocity layer increases and Xiyu conglomerates are developed at the east end of 2D line because of Kuitun River's sedimentation,which is the main reason of energy and S/N reduction of multi-wave seismic data.It is also proved that PS wave is more easily influenced by near surface structure's attenuation than P wave.