【摘要】 将核磁共振T2谱反演问题转化为求目标函数极小值的优化问题,建立新的易于实现T2谱非负约束的优化反演模型,然后利用共轭梯度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、信噪比SNR=25的理论回波数据以及岩心NMR实验数据反演并与构造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,利用反演结果计算的孔隙度与实验室氦孔隙度绝对误差为0.65%。因此,该方法是一种有效和实用的核磁共振T2谱反演方法,具有较强的抗噪能力,能够应用于生产和科研。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.The optimization problem above is solved with the conjugate gradient algorithm.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(RSN)=25 and NMR experimental data of drilling core.The compari-son between the inversion results of this paper and artificial spectrum or the result of software imported in laboratory shows that the method can correctly invert T2 spectrum from artificial NMR data even though RSN=25 and that inversion T2 spectrum with good continuity and smoothness from core NMR experimental data accords perfectly with that of laboratory software,and moreover,the absolute error between the NMR porosity computed from T2 spectrum and helium(He) porosity in laboratory is 0.65%.Hence the T2 spectrum inversion method of conjugate gradient has strong anti-noise ability,is effective and practical for NMR data processing,and can be applied to field production and science research.更多还原