In situ Raman spectroscopic study of diffusion coefficients of methane in liquid water under high pressure and wide temperatures

• In situ Raman spectroscopy was developed to study diffusion process at wide PT ranges.
• Methane diffusion in water was observed from 5 to 40 MPa and 273 to 473 K.
• 19 data of diffusion coefficients were reported at gas reservoir conditions.

Methane is commonly found in sedimentary basin at temperatures of at least 473 K. Accurate values of diffusion coefficients for methane in water at high pressure and elevated temperature are essential to our understanding of transport behavior of methane in pore spaces at reservoir conditions. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusion coefficients of methane in water were determined under high pressures (up to 40 MPa) and wide temperature range (from 273 to 473 K) via Raman spectroscopic method. The relationship between diffusion coefficient of methane in water [D(CH4) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as:D(CH4)=D0TTs−1mwhere D0 = 15.95 × 10−9 m2/s, Ts = 229.8 K, m = 1.8769. At constant temperature, pressure has very small effect on the diffusion coefficients.