Investigation of CO2 Diffusivity in Heavy Oil Using X-ray Computer-Assisted Tomography under Reservoir Conditions

ABSTRACT

Since the 1950’s, the use of carbon dioxide to increase heavy oil recovery has attract more attention from industry and laboratory research. The injection of carbon dioxide has shown technical and economical advantages for enhancing heavy oil and bitumen recovery, because it can effectively reduce viscosity under the reservoir conditions. When carbon dioxide is injected into the reservoir, it partially dissolves into the heavy oil and mass transfer is the first mechanism to occur. Consequently, the accurate prediction and evaluation of the diffusion coefficient of carbon dioxide in heavy oil is one of the key parameters to develop technology for extraction of heavy oil in a feasible and cost-effective way. However, few experimental data for diffusivity of carbon dioxide in heavy oil are available in the literature. Therefore, this study conducted in order to add to the existing the laboratory data for evaluation and calculation of diffusion coefficient of carbon dioxide into heavy oil. In the past, experimental methods used to determine the diffusion coefficient of a gas in heavy oil were conducted under a constant gas pressure, which assumed that oil phase can be contacted with infinite gas at a fixed pressure. In this study, by employing X-ray Computed Assisted Tomography (CAT) and a non-iterative finite volume method, the purpose is to evaluate and compare experimental diffusion coefficients of carbon dioxide in heavy oil under the constant pressure and decaying pressure at the same time. Moreover, investigation of impacts of pressure on diffusion coefficients is conducted.

It is found that the diffusivity of carbon dioxide in heavy oil is sensitive to the system pressure. The comparison between carbon dioxide diffusion coefficients under the constant pressure and those measured under the decaying pressure showed an obvious difference. The results of study are essential for understanding oil recovery through carbon dioxide injection.

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