Relation and Correlation between NMR Relaxation Times, Diffusion Coefficients, and Viscosity of Heavy Crude Oils

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• 作者：Jean-Pierre Korb ; Nopparat Vorapalawut ; Benjamin Nicot ; Robert G. Bryant
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：October 29, 2015
• 年：2015
• 卷：119
• 期：43
• 页码：24439-24446
• 全文大小：478K
• ISSN：1932-7455

文摘

We present a theory and experiments that relate the NMR longitudinal T₁ and transverse T₂ relaxation times to the viscosity 畏 for heavy crude oils with different asphaltene concentrations. The nuclear magnetic relaxation equations are based on a one-dimensional (1D) hydrocarbon translational diffusion in a transient porous network of slowly rotating asphaltene macroaggregates containing paramagnetic species VO²⁺. For heavy crude oils with viscosity 畏 above a certain threshold 畏_c, the effective 1D confinement causes a transition from the usual Stokes鈥揈instein relation for the translational diffusion coefficient D 鈭?1/畏 below 畏_c to a wetting behavior D 鈭?C^te close to the asphaltene aggregates above 畏_c. The theory is compared successfully with the universal viscosity dependencies of relaxation times T₁ and T₂ observed over a large range of viscosities. The theory reproduces the relaxation features of the 2D correlation spectra T₁鈥?i>T₂ and D鈥?i>T₂ for heavy crude oils when varying the asphaltene concentration. This foundation is important because these measurements can be performed down-hole, thus giving a valuable tool for investigating in situ the molecular dynamics of petroleum fluids.