Effects of oligomers dissolved in CO2 or associated gas on IFT and miscibility pressure with a gas-light crude oil system

Abstract The solubility of an oligomer in a supercritical gas solvent (e.g. CO 2 or associated gas (AG) mixture) and the subsequent effects on the phase behavior, interfacial tension (IFT) and miscibility pressure of the in-situ oil/oligomer-thickened gas system at a molecular level are crucial to understanding and designing a thickened miscible gas injection (MGI) process. We have conducted cloud point pressure measurements, which revealed that the phase behavior of P-1-D-thickened CO 2 would follow a UCST (upper critical solution temperature) trend while P-1-D-thickened AG mixture would lie close to a LCST (lower critical solution temperature) behavior. Moreover, our measured equilibrium IFTs of crude oil/P-1-D-thickened CO 2 system and crude oil/PVEE-thickened CO 2 system were found to be slightly lower than those of the crude oil/CO 2 system. This results in a slight reduction in the MMP (minimum miscibility pressure) and considerable reduction in the first contact miscibility pressure (P max ). We found the dissolution of P-1-D in the AG mixture to cause an increase in the equilibrium IFT for the crude oil/P-1-D-thickened AG mixture system, resulting in an increase in both of the MMP and P max . This indicates that the dissolution of an oligomer may have a considerable effect on the crude oil/thickened gas IFT behaviour at a pressure close to the cloud point pressure.