川西坳陷地震波衰减定量估算及分析
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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,resulting in narrow frequency band of reflected seismic data.Hence seiemic resolution can not meet the need of prospecting goals,and low seismic resolution is responsible for stratigraphic 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 component losses of deep layers in western Sichuan basin depression and,as for the marine facies target layers buried deeper than 5000 meters,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.
In western Sichuan basin depression,the marine facies target layers are buried in great depth,resulting in narrow frequency band of reflected seismic data.Hence seiemic resolution can not meet the need of prospecting goals,and low seismic resolution is responsible for stratigraphic 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 component losses of deep layers in western Sichuan basin depression and,as for the marine facies target layers buried deeper than 5000 meters,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.
引文
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[2]李振春,王清振.地震波衰减机理及能量补偿研究综述[J].石油地球物理学进展,2007,22(4):1147-1152
[3]郝召兵,秦静欣,伍向阳.地震波品质因子Q研究进展综述[J].石油地球物理学进展,2009,24(2):375-381
[4]宫同举,孙成禹,彭洪超,等.几种提取品质因子方法的对比分析[J].勘探地球物理进展,2009,32(4):251-256
[5]李庆忠.走向精确勘探的道路[M].北京:石油工业出版社,1994.
[6]钱绍湖,高建华,谷永兴,等.地层吸收衰减模型的制作及补偿方法的研究[J].石油地球物理勘探,1998(S1):18-24
[7]傅朝奎,王建民,王毅军,等.大庆长垣东部地区大地对信号的吸收衰减规律研究[J].石油物探,1998(S1):7-11.
[8]袁子龙,李婷婷.地层吸收衰减与地震仪器记录性能[J].石油物探,2004,43(5):450-452.
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