Mechanistic Study of Gravity-Assisted CO2 Flooding

Abstract

Summary A series of gravity-assisted vertical core displacements of contact-miscible and multiple-contact-miscible CO2/recombined-crude-oil systems was conducted and simulated. Gravity-assisted displacements offer the advantages of eliminating gravity tongues and stabilizing viscous fingers. Although the process has been used successfully in the field, a mechanistic laboratory and modeling study of gravity-assisted multiple-contact-miscible CO2 flooding has not been described previously. The results from this experimental and computer modeling study elucidate the complex mechanisms acting in gravity-assisted CO2 flooding. Component transfer, as occurs in multiple-contact-miscible processes, can strongly affect flood-front stability. In general, better performance is obtained from vertically downward displacements than from comparable displacements in horizontal cores. Miscibility develops at the same pressure in vertical floods and in a much shorter core length. It was further demonstrated that displacement efficiency increases at conditions where mixing of CO2 and oil is minimized. Excellent simulation of experimental recoveries and rates were obtained with a compositional simulator in a one-dimensional (1D) mode.