Evaluation of Polymers as Direct Thickeners for CO2 Enhanced Oil Recovery

Abstract

In this paper, two commercial polymers, poly(vinyl ethyl ether) (PVEE) and poly(1-decene) (P-1-D), are tested to thicken CO2 for CO2 enhanced oil recovery (EOR). First, a series of laboratory tests are conducted to measure the cloud-point pressures of either polymer at different polymer solubilities in supercritical CO2 and the equilibrium interfacial tensions (IFTs) of a light crude oil-pure or polymer-thickened CO2 system under different reservoir conditions. Second, a capillary viscometer is used to measure the viscosities of polymer-thickened CO2 at different test pressures. Third, a total of six high-pressure CO2 coreflood tests are performed to examine the effects of polymer-thickened CO2 on the total CO2 EOR. It is found that at the same and low polymer solubility in pure CO2, the measured cloud-point pressure of PVEE is much lower than that of P-1-D. The measured equilibrium IFT for polymer-thickened CO2 at a high pressure is much lower than that for pure CO2. The PVEE- or P-1-D-thickened CO2 viscosity is approximately (13 to 14) times higher than the pure CO2 viscosity. The CO2 coreflood test results show that PVEE- or P-1-D-thickened CO2 flooding can further enhance oil recovery after a pure CO2 breakthrough. The CO2 breakthrough can be significantly delayed if polymer-thickened CO2 is injected directly.