Asphaltene Precipitation Onsets in Relation to the Critical Dilution of Athabasca Bitumen in Paraffinic Solvents

Current water separation processes associated with oil sands recovery are specifically designed to operate either below or above the critical dilution of bitumen by solvent, defined as the onset of bulk asphaltene precipitation. Oil-water separation for bitumen produced by commercial steam-assisted gravity drainage (SAGD) occurs below critical dilution by water droplets' coalescence. When conducted close to critical dilution, the water separation process for SAGD-produced bitumen faces disruptions attributed to the partial suppression of coalescence and occurrence of agglomeration. In this study, asphaltene precipitation during water separation for SAGD bitumen is investigated with respect to paraffinic solvent addition by using flow-through apparatus for video recording and near-infrared (NIR) spectroscopy at process conditions. The thin liquid film (TLF) technique is employed to determine the effect of solvent-to-bitumen ratio on the properties of the contact zone between two adjacent water droplets in a continuous phase of diluted bitumen. The TLF results highlight changes in the contact zone properties indicative of asphaltene precipitation below the critical dilution detected by NIR spectroscopy. Asphaltene precipitation starts and increases gradually rather than abruptly, contrary to the conventional understanding of critical dilution. On the basis of these findings, it is proposed to consider asphaltene precipitation as a progression rather than a single onset. It is also proposed that the initial onset, termed a surface asphaltene precipitation onset, occurs below critical dilution and is followed by the initial bulk and massive bulk onsets, the latter being closest to critical dilution. The NIR technique effectively detects the initial and massive bulk onsets but cannot detect the surface onset due to observation wavelength limitations. These findings provide valuable insights and directions for addressing recurring issues in bitumen recovery, such as the perceived random occurrence of undesirable stable emulsions due to coalescence inhibition and ineffectiveness of additives in breaking these emulsions.

Automated summary

This study investigates asphaltene precipitation during water separation for SAGD bitumen with the addition of paraffinic solvent. It proposes that asphaltene precipitation is a progression rather than a single onset, starting below critical dilution and gradually increasing. The study also suggests that there are three stages of precipitation: surface asphaltene precipitation onset, initial bulk onset, and massive bulk onset. The NIR technique effectively detects the initial and massive bulk onsets but not the surface onset.