Relation and Correlation between NMR Relaxation Times, Diffusion Coefficients, and Viscosity of Heavy Crude Oils
Relation and Correlation between NMR Relaxation Times, Diffusion Coefficients, and Viscosity of Heavy Crude Oils
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DOI：
10.1021/acs.jpcc.5b07510
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发表时间：
2015-10-29
影响因子：
3.7
通讯作者：
Bryant, Robert G.
中科院分区：
文献类型：
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作者：
Korb, Jean-Pierre;Vorapalawut, Nopparat;Bryant, Robert G.
我们提出了一个理论和实验，与NMR纵向T-1和横向T-2弛豫时间的粘度η与不同的沥青质浓度的重质原油。核磁弛豫方程是基于一维（1D）烃平移扩散的瞬态多孔网络缓慢旋转的沥青质大团聚体含有顺磁性物种VO 2+。对于粘度η高于某个阈值η（c）的重质原油，有效的1D限制导致从通常的平移扩散系数D的斯托克斯爱因斯坦关系（Stokes Einstein relationship）（与低于η（c）的1/η成比例）转变为润湿行为D（类似于接近于高于η（c）的沥青质聚集体的C-te）。该理论比较成功的弛豫时间T-1和T-2在很大的粘度范围内观察到的普遍粘度依赖性。该理论再现了稠油二维相关谱T-1-T-2和D-T-2随沥青质浓度变化的弛豫特征。这个基础是重要的，因为这些测量可以在井下进行，从而为原位研究石油流体的分子动力学提供了一个有价值的工具。
We present a theory and experiments that relate the NMR longitudinal T-1 and transverse T-2 relaxation times to the viscosity eta 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 eta above a certain threshold eta(c), the effective 1D confinement causes a transition from the usual Stokes Einstein relation for the translational diffusion coefficient D proportional to 1/eta below eta(c) to a wetting behavior D similar to C-te close to the asphaltene aggregates above eta(c). The theory is compared successfully with the universal viscosity dependencies of relaxation times T-1 and T-2 observed over a large range of viscosities. The theory reproduces the relaxation features of the 2D correlation spectra T-1-T-2 and D-T-2 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.