Characterization of the viscosity reducing efficiency of CO2 on heavy oil by a newly developed pressurized stirring-viscometric apparatus

Abstract

Dissolution of CO2 in crude oil can change its rheological properties notably, thus implying a broad application prospect in the fields of oil flooding and transportation. In this study, a pressurized stirring-viscometric apparatus was designed based on the stirring-viscometric theory, and the corresponding viscometric method was also proposed. On the basis of the newly developed apparatus and method, the effects of pressure, shear rate and temperature on the apparent viscosity of CO2-heavy oil mixture were probed. It was found that the apparent viscosity of CO2-heavy oil mixture decreases exponentially with the increase of pressure. It only needs the pressure of 2 MPa for the apparent viscosity to decrease dramatically, which is far better than the viscosity-reducing efficiency of N2 under the same condition. Meanwhile, the shear thinning feature becomes more and more obvious with increasing pressure of CO2. Moreover, the viscosity reducing rate of CO2-heavy oil mixture becomes larger with decreasing temperature, while the opposite trend is true for N2-heavy oil mixture. The results of this study provide strong technical support for the feasibility of transporting viscosity-reduced heavy crude oil by CO2.