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Temperature-Dependent Oxygen Effect on NMR D- $$T_2$$ T 2 Relaxation-Diffusion Correlation of n-Alkanes
Applied Magnetic Resonance ( IF 1 ) Pub Date : 2016-09-19 , DOI: 10.1007/s00723-016-0830-4
Igor Shikhov 1 , Christoph H Arns 1
Affiliation  

Nuclear magnetic resonance (NMR) diffusion-relaxation correlation experiments (D-$$T_2$$T2) are widely used for the petrophysical characterisation of rocks saturated with petroleum fluids both in situ and for laboratory analyses. The encoding for both diffusion and relaxation offers increased fluid typing contrast by discriminating fluids based on their self-diffusion coefficients, while relaxation times provide information about the interaction of solid and fluid phases and associated confinement geometry (if NMR responses of pure fluids at particular temperature and pressure are known). Petrophysical interpretation of D-$$T_2$$T2 correlation maps is typically assisted by the “standard alkane line”—a relaxation-diffusion correlation valid for pure normal alkanes and their mixtures in the absence of restrictions to diffusing molecules and effects of internal gradients. This correlation assumes fluids are free from paramagnetic impurities. In situations where fluid samples cannot be maintained at air-free state the diffusion-relaxation response of fluids shift towards shorter relaxation times due to oxygen paramagnetic relaxation enhancement. Interpretation of such a response using the “standard alkane line” would be erroneous and is further complicated by the temperature-dependence of oxygen solubility for each component of the alkane mixture. We propose a diffusion-relaxation correlation suitable for interpretation of low-field NMR D-$$T_2$$T2 responses of normal alkanes and their mixtures saturating rocks over a broad temperature range, in equilibrium with atmospheric air. We review and where necessary revise existing viscosity-relaxation correlations. Findings are applied to diffusion-relaxation dependencies taking into account the temperature dependence of oxygen solubility and solvent vapour pressure. The effect is demonstrated on a partially saturated carbonate rock.

中文翻译:

温度相关的氧气对 NMR D-$$T_2$$ T 2 正构烷烃的弛豫-扩散相关性的影响

核磁共振 (NMR) 扩散弛豫相关实验 (D-$$T_2$$T2) 被广泛用于对石油流体饱和的岩石进行原位和实验室分析的岩石物理表征。扩散和弛豫的编码通过基于流体的自扩散系数区分流体来提供增加的流体类型对比度,而弛豫时间提供有关固相和流体相相互作用以及相关限制几何形状的信息(如果纯流体在特定温度下的 NMR 响应)和压力是已知的)。D-$$T_2$$T2 相关图的岩石物理解释通常由“标准烷烃线”辅助——一种弛豫-扩散相关性,适用于纯正烷烃及其混合物,没有对扩散分子的限制和内部梯度的影响. 这种相关性假设流体不含顺磁性杂质。在流体样品不能保持在无空气状态的情况下,由于氧顺磁弛豫增强,流体的扩散弛豫响应转向更短的弛豫时间。使用“标准烷烃谱线”来解释这种反应是错误的,并且由于烷烃混合物的每个组分的氧溶解度的温度依赖性而进一步复杂化。我们提出了一种扩散-弛豫相关性,适用于解释正构烷烃及其混合物在很宽的温度范围内饱和岩石的低场 NMR D-$T_2$$T2 响应,与大气保持平衡。我们审查并在必要时修改现有的粘度松弛相关性。考虑到氧溶解度和溶剂蒸气压的温度依赖性,研究结果适用于扩散弛豫依赖性。该效应在部分饱和的碳酸盐岩上得到证实。考虑到氧溶解度和溶剂蒸气压的温度依赖性,研究结果适用于扩散弛豫依赖性。该效应在部分饱和的碳酸盐岩上得到证实。考虑到氧溶解度和溶剂蒸气压的温度依赖性,研究结果适用于扩散弛豫依赖性。该效应在部分饱和的碳酸盐岩上得到证实。
更新日期:2016-09-19
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