Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

作者：Philip M. Singer, Zeliang Chen, Lawrence B. Alemany, George J. Hirasaki, Kairan Zhu, Z. Harry Xie, Tuan D. Vo · 发表于：Energy & Fuels · 年份：2018 · DOI：10.1021/acs.energyfuels.7b03603 · 被引用次数：27 · 研究领域：NMR spectroscopy and applications、Hydrocarbon exploration and reservoir analysis、Petroleum Processing and Analysis

One of the much debated mysteries in 1 H NMR relaxation measurements of bitumen and heavy crude oils is the departure from expected theoretical trends at high viscosities, where traditional theories of 1 H– 1 H dipole–dipole interactions predict an increase in T 1 with increasing viscosity. However, previous experiments on bitumen and heavy crude oils clearly show that T 1LM (i.e., log-mean of the T 1 distribution) becomes independent of viscosity at high viscosities; in other words, T 1LM versus viscosity approaches a plateau. We report 1 H 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 (ω 0 /2π = f 0 = 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> ∝ ω 0 independent of viscosity, similar to bitumen. More specifically, on a frequency-normalized scale, we find that T 1LM> × 2.3/ f 0 ≃ 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 1 H– 1 H 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 1 H– 1 H dipole–dipole interactions....