In situ measurement of the dispersion coefficient of liquid/supercritical CO2-CH4 in a sandpack using CT

摘要

Dispersion exists in many scientific and engineering applications, especially for CO2 enhanced gas recovery, which is a vital factor for controlling the contamination of remaining natural gas and gas recovery. In this paper, an in situ method for the dispersion coefficient measurement of liquid/supercritical CO2-CH4 in a sandpack using CT was proposed. The dispersion coefficient in the sandpack was obtained directly from the CO2 mole fraction profiles translated from a CT greyvalue image, which eliminate the deviation caused by the entry/exit effect. The finite difference method, Crank-Nicolson method, was applied to solve the advection dispersion equation for obtaining the dispersion coefficient. The breakthrough profile of the effluent gas was also analyzed and the apparent dispersion coefficient containing the entry/exit effect was measured using the dynamic column breakthrough method. The entry/exit effect enlarged the dispersion coefficient in the range of 14-23% under a water-free experiment according to the deviation between the two methods. And the dispersion coefficient with the sandpack containing residual water was smaller than that of the water-free condition, which was probably caused by the dissolution of CO2 in the displacing frontier into residual water. The dissolution stabilized the dispersion in the displacing frontier and resulted in the reduction of the dispersion coefficient.