Asphaltene Deposition during Bitumen Extraction with Natural Gas Condensate and Naphtha

Abstract

Solvent bitumen extraction processes are alternatives to thermal processes with potential for improved economic and environmental performance. However, solvent interaction with bitumen commonly results in in situ asphaltene precipitation and deposition, which can hinder flow and reduce the process efficiency. Successful implementation requires one to select a solvent that improves recovery with minimal flow assurance problems. The majority of candidate industrial solvents are in the form of mixtures containing a wide range of hydrocarbon fractions, further complicating the selection process. In this study, we quantify the pore-scale asphaltene deposition using two commonly available solvent mixtures, natural gas condensate and naphtha, using a microfluidic platform. The results are also compared with those of two typical pure solvents, n-pentane and n-heptane, with all cases evaluated with both 50 and 100 μm pore-throat spacing. The condensate produced more asphaltenes and pore-space damage than the naphtha and exhibited deposition dynamics similar to that of pentane and heptane. This similarity is due to the presence of a large amount of light hydrocarbon fractions in condensate (∼85 wt % of C5s–C7s) dictating the overall deposition dynamics. Naphtha, which contains heavier fractions (∼70 wt % of C8s–C11s) and aromatic/naphthenic components, generated less asphaltenes and exhibited a slower deposition rate, resulting in less pore damage and overall better performance.