油水双相饱和球形孔隙模型核磁特性

STUDIES ON NUCLEAR MAGNETIC RESONANCE OF SPHERE PORE SPACE SATURATED WITH OIL AND WATER

本文利用特征函数展开方法 ,针对油水双相饱和球形孔隙模型给出了基于扩散效应的核磁共振Bloch控制方程的弛豫模式解表达式。在此基础上给出了油水双相饱和球形孔隙模型的核磁共振特性模拟结果。结果表明 ,孔隙流体的核磁弛豫与孔隙大小、孔隙表面弛豫率、孔隙流体的扩散能力以及含油饱和度等有密切的关系。对于油水双相饱和孔隙 ,在孔隙较小时 ,含油饱和度对弛豫的影响主要表现在弛豫时间随含油饱和度的增加而线性减小 ;但在孔隙较大 ,含油饱和度的增加对弛豫影响表现在两个方面 ,一方面 ,孔隙水弛豫由多个弛豫模式控制逐渐转变为由最小弛豫模式控制。另一方面 ,孔隙水弛豫时间与含油饱和度表现为非线性关系。

In this paper,the basic characteristics of the model spin-spin relaxation has been discussed.Via series expansion method,the Bloch equations controlled by diffusion effect have been solved for sphere pore space geometry saturated with oil and water.From the result,it is found the NMR relaxation is controlled by multi relaxation modes,and associated with pore size,surface relaxation ability,diffusion coefficient of pore fluid and oil saturation.Numerical results have shown that for water-oil two-phase saturated pore space,when pore size is small and as oil saturation increases,the water relaxation time decreases linearly.However,when pore size is relative large,the multi relaxation mode turns to be single mode with the increasing of oil saturation.And at the same time,the variation of relaxation time with oil saturation is non-linearity.