Solubility and diffusivity of carbon dioxide, ethane and propane in heavy oil and its SARA fractions

The design and modeling of solvent based heavy oil recovery requires significant knowledge of the solubility and diffusivity of particular solvents in heavy oil and its fractions. In this study, the original oil was first characterized into saturate, aromatic, resin, asphaltene and maltene fractions (wasp = 0.0 wt. %). Then, an intelligent gravimetric microbalance was used to measure the solubility of carbon dioxide, ethane and propane in Cactus Lake heavy oil and its saturate, aromatic, resin, asphaltene and maltene fractions. The measurements were carried out at 288, 294, 299 and 303 K, and at pressures from 200 to 2000 kPa for carbon dioxide and ethane and up to 600 kPa for propane according to the same temperatures. The Peng-Robinson equation of state was used to correlate the experimental results. The adsorbed amounts of carbon dioxide and ethane in asphaltene were correlated using the Freundlich isotherm.;Diffusion coefficients of carbon dioxide, ethane and propane in heavy oil and its saturate, aromatic and maltene fractions were determined by analyzing time dependent concentration data using a simple diffusion model at 288, 294, 299 and 303 K, and at limited pressure points. Among the three light gases used in this study (carbon dioxide, ethane and propane), carbon dioxide had the lowest diffusivity in heavy oil at the reservoir temperature. The diffusion coefficients of ethane and propane, in the given heavy oil, were close to each other at the reservoir temperature. In general, the diffusivity of light gases in heavy oil and its fractions increased with increasing temperature at constant pressure. The diffusivities of carbon dioxide, ethane and propane in the saturate fractions were higher than in the heavy oil, saturate, aromatic and maltene fractions at reservoir temperature.;As for the given heavy oil sample and its fractions, carbon dioxide showed the lowest solubility among the three gases tested in this study at constant temperature, even at high pressure, when compared to ethane and propane. It was observed the asphaltene content affects the ethane and propane solubility quite significantly in heavy oil at the same equilibrium pressure as compared to carbon dioxide.