地震波跨孔旅行时层析成象分辨率的估计
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摘要
依据费马原理分析了地震波跨孔旅行时层析成象技术对几种简单速度异常体的分辨率，给出了分辨率估算式与数值算例和射线追踪模拟算例。数值算例表明地震波跨孔旅行时层析成象技术的分辨率相当高，特别是对高速异常体和与观测井垂直或斜交的二度异常体的分辨率是如此。对低速异常体而言，存在一个由多种因素决定的临界速度值，当异常体的速度低于此值且走时扰动量不小于走时判读精度时能分辨其轮廓，但不能重建其实际速度场。临界速度值可用以检验射线追踪算法与反演算法的精度。
The evaluating formulas and numerical examples of the possible resolving powef of seismic crowhole traveltime tomography on simple velocity abnormalities are given according to Fermat's principle. The examples show that the possible resolvins power iS much hiSh, specially on high-velocity abnormalities and on 2-dimension abnormalities crossing the hole with a large angle. With regard to lowvelocity abnormalities,there is a critical velocity value which depends on many factors. It is impossible to reconstruct the real velocity distribution when the velocity of abnormality is lower than the critical velocity. A critical velocity can be used to inspect the precision of the ray tracins and inversion algorithm.
The evaluating formulas and numerical examples of the possible resolving powef of seismic crowhole traveltime tomography on simple velocity abnormalities are given according to Fermat's principle. The examples show that the possible resolvins power iS much hiSh, specially on high-velocity abnormalities and on 2-dimension abnormalities crossing the hole with a large angle. With regard to lowvelocity abnormalities,there is a critical velocity value which depends on many factors. It is impossible to reconstruct the real velocity distribution when the velocity of abnormality is lower than the critical velocity. A critical velocity can be used to inspect the precision of the ray tracins and inversion algorithm.
引文
1WilliamsonPR．Aguidetothelimitsofresolutionimposedbyscatteringinraytomography．Geophysics，1991，56（2）：202～2072WilliamsonPR，WorthingtonMH．Resolutionlimitsinraytomographyduetowavebehavior：Numericalexperiments．Geophysics，1993，58（5）；727～735
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