Waylon V. House

Mixing Rules and Correlations of NMR Relaxation Time With Viscosity, Diffusivity, and Gas/Oil Ratio of Methane/Hydrocarbon Mixtures

Viscosity, diffusivity, relaxation time, and gas/oil ratio are important properties in the characterization of reservoirs by nuclear magnetic resonance (NMR) well logging and in prediction of production performance. For the past few years, NMR well logging has been used to estimate formation properties and hydrocarbon liquid/ vapor characterization. Previous work has shown that pure alkanes, alkane mixtures, viscosity standards, and stock tank crude oils have NMR relaxation times that vary linearly with viscosity/ temperature and diffusivity on a log-log scale. However, pure methane at some temperatures and pressures does not follow the same trend. Thus, the linear correlation may not be valid for live crude oils that contain a significant amount of methane. Therefore, the study of methane-hydrocarbon mixtures is of interest. An NMR spectrometer equipped with a high-pressure probe was used to study the relationship between NMR T1 relaxation time and viscosity/temperature, diffusivity, and gas/oil ratio of methane-hydrocarbon mixtures. Relaxation time and diffusivity measurements of three mixtures were made: methane-n-hexane, methane-n-decane, and methane-n-hexadecane. It was found that unlike stock tank oil, relaxation times do not depend linearly on viscosity/temperature on a log-log scale. Each of the mixtures forms a different curve. Generalized correlations between viscosity, diffusivity, gas/oil ratio, and NMR relaxation times were developed. First, the relaxation time mixing rule was developed by studying the theory of NMR relaxation mechanism. From the mixing rule, it was found that departure of relaxation times of methane-n-alkane mixtures from linear correlations on a log-log scale can be correlated with the proton fraction of methane, expressed as gas/oil ratio. Thus, correlations between relaxation time, viscosity/temperature, and gas/oil ratio were developed. Correlations between relaxation time, diffusivity, and gas/oil ratio were also developed. There is a linear relation between diffusivity and viscosity/temperature that is independent of composition. From these correlations, viscosity and gas/oil ratio can be estimated from NMR T1 relaxation time and diffusivity.

Correlations of NMR Relaxation Time with Viscosity, Diffusivity, and Gas/Oil Ratio of Methane/Hydrocarbon Mixtures

Viscosity, diffusivity, relaxation time and gas/oil ratio are important properties in the characterization of reservoirs by NMR well logging and in prediction of production performance. For the past few years, NMR well logging has been used to estimate the formation properties and hydrocarbon liquid/vapor characterization. Previous work has shown that pure alkanes, alkane mixtures, viscosity standards and stock tank crude oils have NMR relaxation times which vary linearly with viscosity/temperature and diffusivity on a log-log scale. However, pure methane at some temperatures and pressures does not follow the same trend. Thus, the linear correlation may not be valid for live crude oils that contain significant amount of methane. Therefore, the study of methane-hydrocarbon mixtures is of interest. An NMR spectrometer equipped with a high-pressure probe was used to study the relationship between NMR T 1 relaxation time and viscosity/temperature, diffusivity and gas/oil ratio of methane-hydrocarbon mixtures. Relaxation time and diffusivity measurements of three mixtures were made, methane-n-hexane, methane-n-decane and methane-n-hexadecane. It was found that unlike stock tank oil, relaxation times do not depend linearly on viscosity/temperature on a log-log scale. Each of the mixtures forms a different curve. Generalized correlations between viscosity, diffusivity, gas/oil ratio and NMR relaxation times were developed. First, the relaxation time mixing rule was developed by studying the theory of NMR relaxation mechanism From the mixing rule, it was found that departure of relaxation times of methane-n-alkane mixtures from linear correlations on a log-log scale can be correlated with the proton fraction of methane, expressed as gas/oil ratio. Thus, correlations between relaxation time, viscosity/temperature and gas/oil ratio were developed. Correlations between relaxation time, diffusivity and gas/oil ratio were also developed. There is a linear relation between diffusivity and viscosity/temperature that is independent of composition. From these correlations, viscosity and gas/oil ratio can be estimated from NMR T 1 relaxation time and diffusivity.

Spin-lattice relaxation and self-diffusion near the critical point of carbon dioxide

Abstract The spin-lattice relaxation time, T1, and the self-diffusion coefficient, D, have been measured in carbon dioxide near the critical point. T1 values are the first for CO2 and this is the third D determination in the critical region. The two previous D determinations, a tracer study conducted by Harris and Duffield (1976) [14] and an NMR study conducted by Krynicki et al. (1981) [20] are in serious disagreement. Harris reported the presence of a strong critical anomaly whereas Krynicki observed that D behaves normally in the critical region. Two isotherms were investigated, 31.06°C and 31.5°C in the density range 0.05ϱc–1.5ϱc. No critical anomaly was found for either T1 or D. This confirms earlier findings on various gases and is in agreement with Krynickis conclusions but stands in contradiction to the findings of Harris. We also had visual confirmation of the approach to the critical point via a sapphire cell connected to the NMR high-pressure probe. The ensemble, NMR probe and sapphire cell, were enclosed in a temperature-controlled air bath.

A corresponding-states correlation of spin relaxation in normal alkanes

Proton spin-lattice T1 and spin-spin T2 relaxation times of the n-alkanes from n-pentane to n-hexadecane were measured at 298.15 K. The T1 measurements essentially agreed with those of Kashaev et al. [1]. No spin-spin relaxation times of the pure alkanes were found in the literature to compare with our data. The temperature dependence of the relaxation rates of these alkanes follow the ratio of the viscosity divided by the temperature. The spin relaxation rate is dedimensionalized using corresponding-states parameters derived from a hindered-rotational model. The resulting three-parameter corresponding-states relationship is found to be closely obeyed by these alkanes.