The horizontal dispersion properties of CO2-CH4 in sand packs with CO2 displacing the simulated natural gas

CO2 sequestration with enhanced gas recovery (CO2-EGR) is a promising technology, especially in the case of re-injecting the separated CO2 from natural gas into the same gas reservoir. The description of dispersion between these two gases benefits for understanding of this miscible displacement and the related reservoir simulation. Here the dispersion properties of CO2-CH4 were studied in short and long sand packs through CO2 horizontally displacing natural gas, both CH4 and one kind of simulated natural gas - SNG (composed of 0.90 CH4 + 0.10 CO2 in mole fraction). We evaluated the effect of gravity and CO2 impurity in SNG on the horizontal dispersion. The gravity effect affected the entry/exit effect and jointly caused the considerably larger dispersion coefficients in the long core than that in the short core. Due to the existence of CO2 impurity, SNG makes itself diffuse into CO2 more easily. Effectively it results in the larger dispersion coefficients. Simultaneously, the horizontal dispersivity of the sand pack calculated as about 0.0161 m in this work, was comparatively larger than the vertical one, resulted from the gravity effect.