柴达木盆地三湖坳陷横波勘探中的低幅异常消除技术

近年来,在柴达木盆地三湖坳陷开展了横波地震勘探,但是由于该区低幅度构造发育,横波静校正引起的"低幅"异常与上述低幅度构造相互混杂,难以区分。为此,针对该区横波表层调查难以控制表层横波速度模型的变化、横波近偏移距初至污染严重、横波折射层发育导致高速界面难以确定等问题,首先采用曲线拟合技术预测污染区横波初至时间确保初至完整性,然后采用面波模型与多层折射分层联合约束反演横波表层速度,最后通过基于速度谱分析的层位匹配建模技术确定合理的横波速度界面,形成了横波表层"低幅"异常消除技术,并进行了现场应用及效果评价。研究结果表明:①曲线拟合技术可以弥补近道污染区横波初至空白,保证层析反演模型的完整性;②基于瑞雷波的频散特性反演建模可以为确定该区浅层横波速度提供可靠的资料,提高浅层模型精度;③面波模型与多层折射分层联合约束反演能够更准确的反演该区表层横波速度场,较好地建立横波速度模型,消除横波剖面上"低幅"异常现象。结论认为,所形成的横波地震勘探低幅异常消除技术消除了横波静校正引起的"低幅"异常现象,提高了横波地震资料的成像品质。

Low-amplitude abnormality eliminating techniques in S-wave seismic exploration in the Sanhu Depression,Qaidam Basin

In recent years, S-wave seismic exploration has been performed in the Sanhu Depression of the Qaidam Basin, but low-relief structures are developed in this area, which are mixed with the "low-amplitude" abnormality caused by S-wave static correction and can be hardly distinguished. In this area, S-wave surface survey can hardly control the variation of the surface S-wave velocity model, the near-offset first arrival of S-wave is seriously contaminated, and the high-velocity interface cannot be determined easily due to the development of S-wave refracting layers. In view of these difficulties, the first arrival of S-wave in the contaminated area was firstly predicted using the curve fitting technique to ensure the integrity of the first arrival. Then, S-wave surface velocity was inverted under the joint constraint of the surface wave model and the multilayer refraction stratification. Finally, the low-amplitude abnormality eliminating techniques used for S-wave velocity interface were determined using the horizon matching modeling technique based on velocity spectrum analysis. What's more, these techniques were applied on site and their application effect was evaluated. And the following research results were obtained. First, the curve fitting technique can compensate the blank first arrival of S-wave in the contaminated area near the trace, so as to ensure the integrity of the tomographic inversion model. Second, the inversion modeling based on the dispersion characteristics of Rayleigh wave can provide the reliable data of the shallow S-wave velocity in this area so as to improve the accuracy of the shallow model. Third, the inversion under the joint constraint of the surface wave model and the multilayer refraction stratification can invert the surface S-wave velocity field in this area more accurately, so the S-wave velocity model can be better established and the "low-amplitude" abnormality in the S-wave section can be eliminated. In conclusion, the proposed techniques for eliminating the low-amplitude abnormality in S-wave seismic exploration can eliminate the "low-amplitude" abnormality caused by S-wave static correction, so as to improve the imaging quality of S-wave seismic data.