Swelling and Viscosity Reduction of Heavy Oil by CO2-Gas Foaming in Immiscible Condition

Abstract

Summary In this study, foaming of heavy oil generated by depressurization from saturated carbon dioxide (CO2) solution was studied because generating foamy oil has a possibility of developing an enhanced oil recovery (EOR). The experiments were carried out by with a heavy crude oil at CO2 pressure less than 10 MPa and a temperature from 20 to 50 °C. The swellings of the generated foamy oils increased from 36.8 to 47.5% with reducing viscosity ratio from 79 to 42%, comparing with original viscosity. Furthermore, the investigation shows that CO2 microbubbles in the foamy oil started nucleating at pressure less than 8.0 MPa during depressurization from the saturation pressure of 9.97 MPa at 50 °C, and the foamy oil started decreasing the apparent viscosity. By exposing generated foamy oil under the shear rate of 76.8 seconds−1 for 5 minutes, the bubble-volume density profile changes from broadband toward to Gaussian distribution caused by disappearing larger size of gas bubbles, where bubble diameter of the maximum probability density of the bubble-volume distribution reduced from 80 μm to less than 10 μm. However, reduction of viscosity ratio was almost kept even though the distribution was changed; this shows that apparent viscosity strongly depends on the microbubbles sized less than 10 μm in diameter. It was expected that CO2 foamy oil has a potential to improve the recovery ratio of heavy oil by making the residual oil flow out from the immobile zones because of its large apparent swelling and improving mobility in porous oil-flow.