Measurements of diffusion coefficient of methane in water/brine under high pressure

Abstract

The diffusion coefficient of methane in water plays an important role in the formation and dissociation of methane hydrate. However, most of the previous studies on the diffusion coefficient of methane in brine are performed at room temperature and low pressures, which is quite different from the formation condition of methane hydrate. In this study, we measure the diffusion coefficient of methane in pure water and brine in capillary tube at 10.3 MPa and temperature ranging from 283.15 to 308.15 K. We use the Raman spectrum to measure the ratio of C-H bound signal of methane to the O-H bound signal of water, to estimate the concentration of methane dissolves in water/brine. The Raman spectrum is collected at different time and different positions away from the liquid-gas interface. Diffusion coefficient is determined by fitting the experimental data with the concentration profiles solved from Fick's second law and semi-infinity boundary condition. By this method, we can evaluate the diffusion coefficient at different temperatures or salinities. The diffusion coefficient of methane in water/brine increases as the temperature increases. The diffusion coefficient of methane in brine is lower than that in pure water. Molecular dynamics (MD) simulation is also performed in this study to calculate the diffusion coefficient of methane in water/brine. The MD results can successfully predict the tendency of temperature effect and adding electrolyte.

Reactive Transport Modeling of Natural Gas Molecular and Isotopic Evolution During Diffusive Transport in the Subsurface

“…The D 0-C1 range was determined by considering the variability in published values. For the low value, D 0-C1 was reduced by 8% compared to the base case to match the data from Chen et al (2018). For the high value, the D 0-C1 was increased by 20%, consistent with the results of Pokharel et al (2017).…”

“…Pressure dependence of diffusion coefficients is not implemented in PHREEQC. Chen et al (2018) found that the diffusion coefficient for methane was insensitive to pressures up to 100 atm. Therefore, it was assumed that pressure does not affect the D 0 of C 1 , C 2 , and C 3 .…”

Diffusion coefficients at infinite dilution of carbon dioxide and methane in water, ethanol, cyclohexane, toluene, methanol, and acetone: A PFG-NMR and MD simulation study

“…Fewer data are available for CO 2 in ethanol [35,10,11,36,37,29,38], cyclohexane [39], toluene [10,40,41], methanol [35,10,11,19,31,42], and acetone [10]. For CH 4 , diffusion coefficients have been investigated before in water [8,43,9,44,45,46,47,48,34].…”

Diffusion Coefficients of Methane in Methylbenzene and Heptane at Temperatures between 323 K and 398 K at Pressures up to 65 MPa

“…Several measurement techniques have been applied including the Taylor dispersion technique, NMR, pressure-time measurements and also chromatographic analysis from a diffusion cell. The diffusion coefficients of methane in water have also been thoroughly investigated experimentally and mathematically using methods such as the capillary cell method, the diaphragm method, the inverted tube method, the modified barrier method and a simplified method where the capillary tube was used with in situ Raman spectroscopy [28][29][30][31][32][33][34][35][36][37]. Other studies on the diffusion of methane in liquid hydrocarbons have focused on heavy crude oils and bitumen [38][39][40][41].…”