Pore-level visual investigation of miscible and immiscible displacements

Abstract

The mechanisms of oil recovery by gas injection, with particular interest in the generation of highly viscous oil residues and asphaltene flocculation and the resulting permeability impairment, have been studied. The flow visualisation experiments were performed in high pressure heterogeneous micromodels reproduced from real rock micrographs. The visual micromodels were also employed in series with a compatible glass bead pack. Displacement experiments simulating secondary and tertiary recovery of a North Sea crude oil at 27.5 MPa and 33°C were conducted. Methane, propane and water were injected. The displacement video observations and the measurements made are presented. The pore-level investigation of immiscible gas drive revealed the importance of wettability and capillary pressure on the spontaneous movements of the fluid interfaces. Fractions of pores occupied by oil become oil-wet. Thin films of oil on these segments keep the oil phase continuous and results in the flow and recovery of oil trapped in narrow sections of the pores, even at very low capillary numbers. Further observations on oil, gas and connate water movements are also presented. Miscible displacement of oil with propane did not induce any significant precipitation of asphaltenes in pores. However, bulk mixing of propane and oil can promote asphaltenes flocculation, pore plugging and permeability impairment. The deposited materials can be partially dissolved and removed by contacting with fresh oil.