title: Temperature-Dependent Oxygen Effect on NMRD-[Formula: see text] Relaxation-Diffusion Correlation ofn-Alkanes.
abstract: Nuclear magnetic resonance (NMR) diffusion-relaxation correlation experiments (D-[Formula: see text]) 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 ofD-[Formula: see text] 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 NMRD-[Formula: see text] 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.
authors.affiliation: School of Petroleum Engineering, The University of New South Wales, Sydney, NSW 2052 Australia.
authors.forename: Igor
authors.initials: I
authors.lastname: Shikhov
authors.affiliation: School of Petroleum Engineering, The University of New South Wales, Sydney, NSW 2052 Australia.
authors.forename: Christoph H
authors.identifier: 0000-0003-1721-3996
authors.initials: CH
authors.lastname: Arns