【摘要】 基于模型构制思想将核磁共振T2谱反演问题转化为求目标函数极小值的最优化问题,建立新的易于实现T2谱非负性约束的优化反演模型,然后利用共轭梯度FR算法解决上述反演问题。将该方法应用于无噪声理论回波数据反演、信噪比SNR=25的理论回波数据反演以及岩心NMR实验数据反演,并与真实谱及实验室国外软件反演结果对比表明,无噪声理论回波数据反演的T2谱与构造谱几乎完全符合;信噪比SNR=25时反演的T2谱和构造谱符合得很好;岩心反演的T2谱与实验室国外软件反演的T2谱符合得很好,谱线光滑连续。利用反演结果计算的核磁孔隙度与实验室氦孔隙度绝对误差为0.65%。更多还原

【Abstract】 Based on the optimization techniques,the T2 spectrum inversion method of conjugate gradient that is easy to realize non-negativity constraint of T2 spectrum is proposed.The method transforms the linear mixed-determined problem of T2 spectrum inversion into the typical optimization problem of searching the minimum of objective function by building up the objective function according to the basic idea of geophysics modeling.The optimization problem above is solved with the conjugate gradient algorithm that has quick convergence rate and quadratic termination.The method has been applied to the inversion of noise free echo train generated from artificial spectrum,artificial echo train with signal-to-noise ratio(SNR)=25 and NMR experimental data of drilling core.The comparison between the inversion results of this paper and artificial spectrum or the result of software imported in NMR laboratory shows that the method can correctly invert T2 spectrum from artificial NMR relaxation data even though SNR=25 and that inversion T2 spectrum with good continuity and smoothness from core NMR experimental data accords perfectly with that of laboratory software imported,and moreover,the absolute error between the NMR porosity computed from T2 spectrum and helium(He) porosity in laboratory is 0.65%.更多还原