Abstract

Solvents can be injected to dilute viscous heavy oil or bitumen and improve the recovery of the vast reserves of heavy oil and bitumen in Canada. In an evolution of the SAGD and VAPEX processes, some new schemes that use solvent and steam appeared to offer a more economical and environmentally sound alternative to extract heavy oil and bitumen compared to SAGD alone. Mass transfer rates determine whether these solvent-assisted processes are feasible for heavy oil and bitumen recovery. The solvent-bitumen diffusion coefficient is a basic parameter needed. According to previous literature, the effective diffusion coefficient in porous media is much smaller than the true diffusion coefficient in bulk fluids. However, good-quality data from diffusion experiments of heavy oil and hydrocarbon solvent systems for effective diffusion coefficients determination in porous media is still scarce. This paper presents diffusion experiments of liquid solvent in heavy oil saturated sand using X-ray Computer Assisted Tomography (CAT), and determines the effective diffusion coefficients based on an updated approach, which considers porosity variation of porous media and volume changes on mixing. In addition, the relationship between the effective diffusion coefficient of solvent in oil saturated sand pack and the true diffusion coefficient in bulk fluids is investigated.

Introduction

For the recovery of the vast reserves of heavy oil and bitumen in Canada, some new hybrid steam-solvent processes 1 were proposed recently and were developed to offer the possibility of higher oil production rates and recoveries, but less energy and water consumption than SAGD. These methods come by the names of Expanding Solvent SAGD (ES-SAGD), Solvent Aided Process (SAP), Liquid Addition to Steam for Enhancing Recovery (LASER), Steam Alternating Solvent process (SAS) and Thermal Solvent Hybrid Process. Hopefully these solvent-assisted processes will become more mature and will be gradually applied in the field, thus improving the recovery of heavy oil and bitumen. In order to study these mass transfer processes in porous media quantitatively, the diffusivity of solvent in heavy oil should be investigated further.

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