Figure 1—The gap between immiscible viscous fingering and
miscible viscous fingering.
Suzuki et al. (2016) noted in their study with sodium sulfate and
polyethylene glycol that the phase separation via spinodal decomposition
outside the stage of metastability is associated with multiple droplet
formation (due to the thermodynamic instability as opposed to
hydrodynamic instability). Following their study, Fu et al. (2017)
reported in their study of gas-in-oil injection for enhanced oil
recovery at high-pressure conditions, the transition of the fluid system
from immiscible to partially-miscible results in higher occurrences of
droplet formation than finger formations.
This leads us to a question regarding one of the rarely studied but
commonly encountered case: What about emulsions ? Emulsions are
defined as fluid systems that consist of the oleic phase and aqueous
phase and can achieve mixing with the addition of surface-active agents.
Even without the addition of chemicals, emulsification is a commonly
encountered part of crude oil production (Lee et al. 2019; Bruns and
Babadagli 2020; Wang et al. 2020)— especially in the case of bitumen
as bitumen contains a higher level of indigenous surface-active
components such as asphaltene, naphthenic acid, humic acid, etc.
relative to the light crude.
In our recent study (Lee et al. 2020), we have provided an extensive set
of visual images captured from emulsion visualization experiments, where
a heavy oil-saturated Hele-Shaw model was injected with chemicals of
various components and rheological properties—which allows us to
categorize and capture the universal fundamentals of the chemically
induced viscous fingering development. The compact view of the original
experimental images of selected samples is available in Figure
2 which displays the viscous finger development with chemical addition
including AS (alcohol propoxy sulfate), CTAB, SiO2, and
XG (Xanthan gum). The classification methods for the finger morphologies
are elaborated in the cited study.