PHASE-BEHAVIOR AND CHEMICAL FLOODING PROPERTIES OF WATER-OIL-NONIONICAMPHIPHILE MIXTURES

The relationship between phase behaviour and mobilisation of residual oil using Bentheimer cores has been investigated for the system: water -n-decane - nonionic surfactant (C12E5). A part of the phase prism fo r the system (temperature as the z-coordinate) has been determined. Ad ding 500 ppm polymer increases the system hydrophobicity corresponding to approximately 5 degrees C. Recoveries of residual oil after waterf looding by surfactant flooding, oil cuts, pressure-drop profiles, and endpoint relative permeabilities have been determined for 17 experimen ts. In addition, determination of the surfactant retentions has been p erformed for eight of these flooding experiments. The flooding experim ents were conducted varying the phase behaviour, flood rate, and wetta bility conditions of the cores. For water-wet cores, it is shown that mobilisation of the residual oil is correlated to the interfacial tens ion and the capillary number, and that it is independent of II-, III a nd II+ phase behaviour. In mixed-wet cores, the highest recovery was f ound when flooding with a system having II+ phase behaviour. It is pro bable that solubilisation of the surfactant in the residual oil and a film displacement mechanism caused the high recovery in the mixed-wet cores at II+ phase behaviour.