One of the much debated mysteries in ¹H NMR relaxation measurements of bitumen and heavy crude oils is the departure from expected theoretical trends at high viscosities, where traditional theories of ¹H–¹H dipole–dipole interactions predict an increase in T₁ with increasing viscosity. However, previous experiments on bitumen and heavy crude oils clearly show that T_1LM (i.e., log-mean of the T₁ distribution) becomes independent of viscosity at high viscosities; in other words, T_1LM versus viscosity approaches a plateau. We report ¹H NMR data at ambient conditions on a set of pure polymers and polymer–heptane mixes spanning a wide range of viscosities (η = 0.39 cP ↔ 334 000 cP) and NMR frequencies (ω₀/2π = f₀ = 2.3 MHz ↔ 400 MHz) and find that at high viscosities (i.e., in the slow-motion regime) T_1LM plateaus to a value T_1LM> ∝ ω₀ independent of viscosity, similar to bitumen. More specifically, on a frequency-normalized scale, we find that T_1LM> × 2.3/f₀ ≃ 3 ms (i.e., normalized relative to 2.3 MHz), in good agreement with bitumen and previously reported polymers. Our findings suggest that in the high-viscosity limit T_1LM> and T_2LM> for polymers, bitumen, and heavy crude oils can be explained by ¹H–¹H dipole–dipole interactions without the need to invoke surface paramagnetism. In light of this, we propose a new relaxation model to account for the viscosity and frequency dependences of T_1LM and T_2LM, solely based on ¹H–¹H dipole–dipole interactions. We also determine the surface relaxation components T_1S and T_2S of heptane in the polymer–heptane mixes, where the polymer acts as the “surface” for heptane. We report ratios up to T_1S/T_2S ≃ 4 and dispersion T_1S(ω₀) for heptane in the mix, similar to previously reported data for hydrocarbons confined in organic matter such as bitumen and kerogen. These findings imply that ¹H–¹H dipole–dipole interactions enhanced by nanopore confinement dominate T_1S and T_2S relaxation in saturated organic-rich shales.

中文翻译：

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使用聚合物-庚烷混合物解释沥青和有机页岩中的NMR弛豫

一个在许多争论奥秘^1个沥青和重质原油的1 H NMR弛豫测量是从在高粘度，其中的传统理论预期的理论趋势出发^1个H- ¹ ħ偶极-偶极相互作用预测的增加Ť ₁随粘度。然而，先前在沥青和重质原油上的实验清楚地表明，在高粘度下，T _1LM（即T ₁分布的对数均值）变得与粘度无关。换句话说，T _1LM与粘度的关系趋于平稳。我们报告¹在环境条件下在一组纯的聚合物和聚合物-庚烷混合物跨越宽范围的粘度（η= 0.39厘泊↔334 000厘泊）和NMR频率（ω的1 H NMR数据₀ /2π= ˚F ₀ = 2.3兆赫↔400兆赫）并且发现，在高粘度（即，在慢动作制度）Ť _1LM高原的值Ť _1LM> αω ₀独立粘度的，类似于沥青。更具体地，在频率归一化的比例，我们发现，Ť _1LM> ×2.3 / ˚F ₀ ≃3毫秒（即，相归一化到2.3兆赫），较好的一致性与沥青和先前报道的聚合物。我们的发现表明，在高粘度范围内Ť _1LM>和Ť _2LM>用于聚合物，沥青和重质原油可通过说明^1个H- ¹ ħ偶极-偶极相互作用，而不需要调用表面顺磁性。鉴于此，提出了一种新的弛豫模型以便考虑的粘度和频率依赖性Ť _1LM和Ť _2LM，仅基于^1个H- ¹ H ^偶极-偶极相互作用。我们还确定了聚合物与庚烷混合物中庚烷的表面弛豫成分T _1S和T _2S，其中聚合物充当庚烷的“表面”。我们报告的比率不超过Ť _1S / Ť _2S ≃4和分散Ť _1S（ω ₀），用于在庚烷混合，类似于先前报道的在有机物局限于烃如沥青和油母岩质的数据。这些发现暗示，^1个H- ¹通过纳米孔限制支配增强ħ偶极-偶极相互作用Ť _1S和Ť _2S松弛饱和富含有机物页岩。