Gas Solubility, Viscosity And Density Measurements For Athabasca Bitumen

Abstract

Abstract New data on density and gas-solubility for Athabasca bitumen are presented for CO2, CH4 and N2. The apparatus of Jacobs for saturating bitumen with a gas provided reliable viscosity measurements. This apparatus was modified to permit the isolation and removal of gas-saturated bitumen samples for solubility measurements. The solubility measurements were performed on a controlled depressurization set-up. The range of temperatures for these data is 25°C to 100°C; the pressure was varied up to 10 MPa. It was observed that CO2 has high solubility in bitumen and causes tremendous reductions in viscosity. The solubility of nitrogen is quite low, whereas that of methane is intermediate. Introduction A knowledge of the physical properties of the oil present in Alberta tar-sands is required to mathematically model and simulate the processes used for the recovery of tar-sands. The data on gas-solubility, viscosity, and density for gas-saturated bitumen are of special importance to the in-situ techniques, such as CO2 injection and fire-flooding, that are now being actively pursued. Viscosity data for Athabasca bitumen (the dead oil) and the bitumen saturated with carbon dioxide (live oil) were presented by Jacobs(1). Data from similar experiments using methane and nitrogen gases were published subsequently by Jacobs and coworkers(2). The need existed, however, for the solubility data for these gases. Also needed were methods for correlating temperature and pressure with the viscosity and gas-solubility of bitumen. Experimental data for CO2, CH4 and N2 gases are presented in this paper. A successful first attempt at correlating these data is presented elsewhere(3). The viscosity of gas-saturated oils (live oils) depends on the type of gas, bitumen composition temperature and pressure. The qualitative relationship among the individual variables for a given gas and bitumen is such that the viscosity decreases with increasing temperature and decreasing pressure. It is generally understood that the above changes in pressure and temperature cause a reduction in the amount of dissolved gas. Hence, the smaller the amount of dissolved gas the less the extent of viscosity reduction. In other words, the significance of system pressure and temperature manifests itself not only in the dead oil viscosity, but also in the amount of dissolved gas (more gas being dissolved at higher pressures and lower temperatures). The dead oil viscosity is known to decrease significantly with temperature and to remain more or less unchanged with pressure. The live oil viscosity, on the other hand, decreases with the saturation pressure and temperature. The effect of temperature on live oil viscosity is less sharp than for the dead oil under the same condition. For both temperature and pressure, the live oil viscosity reflects a combination of opposing effects, of which one is more dominant than the other, Obviously, the quantitative description of the bitumen viscosity behaviour is a complex matter. Ward and Clark(4) were the first to make extensive viscosity and density measurements on bitumens, Jacobs(l) and Jacobs et al.(2) measured the viscosity of dead and live oils saturated with CO2, CH4 and N2 over a range of temperature and pressure.