Determination of Diffusion Coefficient During Gas Injection in Heavy Oil Hydrocarbons

An essential transport characteristic that links a substance's molar (mass) flux to its concentration gradient is the molecular diffusion coefficient. For modeling and performance forecasting of solvent-aided recovery processes of heavy oils such as VAPEX and SAGD; a reliable and accurate estimation of the molecular diffusion coefficient is a crucial input. Despite the importance of this parameter, there is no approved way to measure it, especially in systems with heavy oil and gaseous solvents that have limited solubility. This can be as a result of the intricacy of experimental measures and the challenge of analyzing experimental data. There are two direct and indirect methods for measuring the diffusion coefficient, the direct method has not been addressed because it is expensive and time-consuming. Indirect methods include Constant-Volume Methods (Pressure Decay), Constant-Pressure, Refractive Index, Nuclear Magnetic Resonance (NMR), X-ray Computer-Assisted Tomography (CAT), Pendent drop and Microfluidics. The advantage and disadvantages of these experimental methods established for diffusivity measurements of the gaseous solvent in heavy oil systems are discussed in this article. According to the investigations carried out in this study, the Constant-Volume Methods (Pressure Decay) with the least error percentage (۱.۰۵%) was chosen as the best method for measuring the diffusion coefficient. The diffusion coefficient of light and heavy oil was compared, and light oil has a higher diffusion coefficient.

Keywords:

Heavy oil , Diffusion coefficient , diffusivity , gas injection