川西坳陷地震波衰减定量估算及分析  

QUANTITATIVE CALCULATION AND ANALYSIS OF SEISMIC WAVE ATTENUATION IN WESTERN SICHUAN BASIN DEPRESSION

作　　者：涂远艮[1] 王达远[1] 李华科[1] 

机构地区：[1]中国石化西南油气分公司勘探开发研究院,四川成都610000

出　　处：《物探与化探》2013年第4期596-602,632,共8页Geophysical and Geochemical Exploration

摘　　要：川西坳陷海相勘探目的层埋藏较深,反射资料频带窄,地震分辨率无法满足勘探要求,地层吸收衰减是导致分辨率低的主要原因,为了解深层地震波的衰减情况,首先根据低降速带资料和测井资料建立川西坳陷地层模型,然后定量估算球面扩散、吸收衰减和透射损失引起的地震波衰减量,以估算的衰减值为参考,同时结合地震采集资料、井中零偏VSP和Walkway-VSP资料来分析影响深层反射波高频信号接收的因素。分析指出1 500 m以上浅层强吸收衰减是造成川西坳陷深层反射波高频成分缺失的主要原因,5 000 m以下海相地层反射波频带只能达到40Hz左右,深层资料采集应以降低背景干扰为重点,并在提高资料采集密度上下功夫,以达到增强深层弱反射信号、提高地震勘探精度的目的,而不应单纯强调提高分辨率。In western Sichuan basin depression, the marine facies target layers are buried in great depth, resuhing in narrow frequency band of reflected seismic data. Hence seiemic resolution can not meet the need of prospecting goals, and low seismic resolution is re- sponsible for stratigrapbic absorption attenuation. In order to understand completely the reason for the attenuation of seismic waves, the authors built a model for western Sichuan basin depression strata, then calculated quantitatively spherical divergence, absorption and transmission attenuation of seismic wave based on the model, and combined the calculated attenuation values with seismic data, VSP and Walkway-VSP data to analyze the factors affecting high frequency reflected signal acquisition recording of deep layers. It turns out that the serious absorption attenuation of shallow strata above 1500 meters is the fundamental cause responsible for high frequency com- ponent losses of deep layers in western Sichuan basin depression and, as for the marine facies target layers buried deeper than 5000 me- ters, field acquisition data can only reach about 40Hz frequency band. Therefore, the field acquisition methods aiming at deep target layers should focus on reducing background noises and increasing acquisition density to enhance weak reflection signals of deep layers so as to improve the seismic prospecting precision, rather than solely focus on improving the seismic resolution.

关 键 词：地震波 吸收衰减 品质因子 球面扩散 VSP 

分 类 号：P631.4[天文地球—地质矿产勘探]