Study on density of the supercritical methane

The density of supercritical methane is not only an important parameter for calculation of unconventional natural gas resources and adsorption capacity of methane in coal, but also a main indicator for measurement of the diffusion efficiency of supercritical methane and the ability to dissolve organic matter. Through analysis and comparison of the applicability of various gas state equations, it is realized that the Helmholtz energy state equation can accurately calculate the density of methane under the conditions of 0-30 MPa and 270-360 K. A calculation program for methane density was written using Microsoft Office Excel, and the error was less than 0.05% compared with NIST commercial software. Finally, the changing of methane density was analyzed. In the range of 0-100 MPa and 270-360 K, the density of methane increases with the increase of pressure. The increase rate is greater before 30 MPa and the sensitivity to temperature is strong. Afterwards, the growth rate gradually slows down, while the sensitivity decreases. Under the in-situ condition of the coal seam, with the increase of buried depth, the density increases with temperature and decreases with pressure. Under the combined action of temperature and pressure, the density of methane first increases approximately linearly, and the growth rate gradually decreases. The results provide basic parameters for the occurrence and potential prediction of deep CBM.