Estimation of Diffusion Coefficients in Bitumen Solvent Mixtures Using X-ray CAT Scanning and Low Field NMR
Wen, Y., Kantzas, A. and Wang, G.
CIM 2004-064 presented at the 55th Annual Technical Meeting of the Petroleum Society held in Calgary, June 8-10, 2004;
5th International Conference on Petroleum Phase Behaviour and Fouling, Banff, Alberta, June 13-17, 2004.
Diffusion plays an important role in both VAPEX and Solvent Injection processes for oil/bitumen recovery. In this paper, X-ray CAT scanning and low field NMR have been used to obtain experimental data for the diffusion of several solvents in bulk bitumen.
Low field NMR has been used successfully in determining both solvent content and viscosity reduction in heavy oil and bitumen mixtures with various solvents. NMR is also a potential tool for diffusion coefficient measurement in solvent bitumen system (1). In this paper, the results of diffusion coefficient calculated from NMR is further discussed and compared with the results obtained from X-ray CAT scanning.
X-ray CAT scanning takes advantage of density contrasts in the scanned sample through the measured CT number. With solvent diffusing into heavy oil or bitumen, the CT number changes during the process and provides the corresponded density of the mixture. Therefore, the concentration gradient distribution with distance can be obtained. A Fick type of equation can be written and an apparent diffusion coefficient can be calculated. This approach and the results of this analysis are presented along with an evaluation of the applicability of the assumptions in Fick’s Law.