Rheology and diffusivity of bitumen with liquid and supercritical CO2

Carbon dioxide (CO2) sequestration in depleted reservoirs is a practical solution to mitigate the emission of greenhouse gases. In financial considerations of the CO2 sequestration projects, CO2 can be considered as a solvent which can mobilize stranded oils underground. In this paper, we apply our novel high-pressure rheometry coupled with the pressure-decay technique, developed in our previous studies, to precisely determine the viscosities and mutual diffusivities for mixtures of bitumen with CO2 at the temperature range of 30 degrees C-110 degrees C and at pressures as high as 10 MPa, where CO2 is in liquid or supercritical forms. The developed novel technique overcomes the shortcomings of the pressure decay method by significant reduction in the experimentation time and eliminating uncertainties in determining the equilibrium pressure values. The reduced variable model is successfully adopted to describe the effects of temperature, pressure and CO2 concentration on the viscosity of the mixtures. The viscosity data for the mixtures show a continuous drop regardless of the state of CO2. Unlike the viscosity values, the diffusivity of CO2 into the bitumen is dependent on the state and pressure of CO2. The diffusivity values increase with temperature which are well described by the Arrhenius equation. While pressure had a significant effect on the diffusivity values in the gaseous state, shown in our previous study, the diffusivity values are less sensitive to pressure in the liquid and supercritical forms. It is also found that liquid CO2 has the highest diffusivity in bitumen compared to supercritical and gaseous CO2. The diffusivity values were compared to the few data in the literature for pressures above 10 MPa for CO2-bitumen mixtures.