Low-Field and Online NMR for Detection of Fluid Molecular Structure

Fluid molecular structure can be determined by low-field and online nuclear magnetic resonance (NMR). Overcome the disadvantages of traditional laboratory fluid analysis methods, such as low efficiency, the variability of physical parameter, easily contaminated samples, etc.
Studies have shown that τ c has direct correlation with molecular weight (Mw) [1]. In previous work we have developed viscosity prediction method of crude oils from NMR relaxations times [2]. With the relationship between NMR relaxation time and τc known, the relation between NMR relaxation and η can be obtained once the relation between τc and η is established. After the η of crude oils measured, Mw can be searched from American National Standard (ANSI/ASTM D2502-2004). The correlation of η, τc and Mw can be obtained by exponential fitting the experimental results.
The distance b between 1H on the same position of molecule varies with the specific molecular structure.

The difference in b values will produce a certain impact on the relation between relaxation time and τc. To precisely establish the relationship between relaxation time and τc, the method is to remove the influence of b to obtain the relationship between T1/T2 and τc. The T1/T2 distribution can be measured by DEFIR pulse sequence, so we can obtain reorientation time τc distribution of the sample. Then we can acquire longitudinal relaxation time expression and get b distribution of sample.