Pore-scale analysis of condensing solvent bitumen extraction

•Liquid solvent left more residues comparing with the vapor chamber.•Butane-in-residue emulsions generated during butane runs intensified pore plugging.•Residuals in liquid zone were majorly asphaltenes as they exhibited low fluorescence.•Bitumen recovery was most vigorous at the condensing edge due to multi-phase flow. Current thermal methods for bitumen recovery are effective but require both environmental and economic performance improvements. Light hydrocarbon solvent injection is an alternative to steam injection that has the potential to reduce greenhouse gas emissions associated with recovery. However, the pore-scale behavior of the solvent-bitumen system is very complex and poorly characterized to date. In this work, a high-pressure high-temperature micromodel with reservoir-relevant geometry combined with imaging tools provides a pore-scale window into solvent injection methods using propane and butane. The combination of two-phase dynamics and solvency at the condensing edge leads to significant bitumen production, similar in both propane and butane injections. In the liquid zone ahead of the condensing edge, butane results in dense, small, and immobile solvent-in-residue emulsions. In contrast, liquid propane produced larger emulsions with some mobility. Spectroscopy combined with fluorescence imaging indicated that the residual immobile emulsions in the butane case are bitumen heavy fractions, and largely asphaltenes. Collectively this work highlights the distinct recovery mechanisms and limitations at both the condensing front and liquid zone for these common solvents.