松辽盆地北部地区地震虚反射对分辨率的影响分析

Analysis of the Effect of Seismic Ghost Reflection on Resolution in the North Songliao Basin

理论研究表明虚反射会降低分辨率。因此,在井深设计时,爆炸点尽可能靠近波阻抗界面(潜水面界面),但是,在实际地震采集工程中,单从理论出发使炸药非常靠近波阻抗界面,结果会使爆炸后产生的破坏带炸穿波阻抗界面,使一部分上行波上传形成面波、声波等干扰,减少激发能量向地下传播。本文从虚反射地震波的频率响应分析出发,考虑表层反射系数、吸收衰减、几何扩散等因素影响,结合松辽盆地北部地区表层结构调查结果,对表层虚反射影响进行分析研究。提出了在考虑地层的吸收衰减、几何扩散的情况下,虚反射作用对有效反射波不会造成较大影响,相反,只要井深设计合理,虚反射对有效反射波起到相干加强的作用,对高分辨率地震勘探是有利的。说明了井深设计无需过多考虑虚反射影响,着重考虑药柱长度和爆炸破坏带范围,保证波阻抗界面不受破坏,使激发能量较多的向地下传播。

Theoretical research suggests that the ghost reflection reduces the seismic resolution. Therefore, in designing well depth, the shot point shall approach the wave impedance interface as much as possible. However, during the practical seismic acquisition, If the dynamite approaches closely the wave impedance interface theoretically, the outburst will tear into the interface, which will make a part of upgoing waves that will bring such interference waves as surface wave and sound wave. The interference waves will impede the activated energy to be transmitted to the underground. The paper analyzes the effect of ghost reflection in the surface layer in the North Songliao Basin by taking an account of the surface reflection coefficient, absorptive attenuation, geometric spreading and other factors and integrating the survey on the surface structure. The study shows that the ghost reflection will not affect the effective reflection wave greatly if the absorptive attenuation and geometric spreading in the formation are included. On the contrary, as long as the design of well depth is good, the ghost reflection will be helpful to the hi-resolution exploration. The analysis suggests that the well depth design will not be taken into too much consideration and the most important is about the length of dynamite column and the range of outburst.