Laboratory experiment of CO2–CH4 displacement and dispersion in sandpacks in enhanced gas recovery

Abstract

A laboratory investigation was performed to describe the detailed CO2–CH4 displacement and dispersion in enhanced gas recovery. A series of experiments were conducted in a vertical sandpack sample of glass beads at a core pressure in the range of 4–14 MPa at temperature of 29–60 °C with a CO2 injection flow rate of 0.2–0.5 ml/min. The displacement process was scanned with a resolution of approximately 34.2 μm by an X-ray CT scanner in this study. The porosity distribution of the sandpack sample was obtained along the core based on the CT image. Simultaneously, the existence of the mixing zone was proven, and no interface appeared in the process of CO2–CH4 displacement. Furthermore, the dispersion coefficients were obtained by analysing the produced gas. The experimental results revealed that the dispersion coefficient increased with temperature exponentially in our experimental ranges, which can be interpreted by molecular kinetic theory. The dispersion coefficient becomes much larger as the pressure becomes closer to the critical pressure at 40 °C, which is probably enhanced by the fluctuation phenomenon, as the CO2 density sharply changes with the pressure around the critical point. In addition, the dispersion coefficient increases with the flow rate. The heterogeneity of sandpack sample packed with BZ2 glass beads leads to a larger dispersion coefficient, whereas the growth trend in other samples is not obvious. Ultimately, the dispersivity of the BZ04 glass beads sandpack sample is estimated at 0.002–0.0055 m based on the dispersion coefficient data.