Correlations of viscous fingering in heavy oil waterflooding

• Three distinct regions of viscous fingering in heavy oil waterflooding are proposed.
• Numerous small fingers in early stage degenerate into a single finger at later stages.
• Number of fingers is not flowrate-dependent and it grows with square root of time.
• Finger width is comparable with pore size and length/width increase in early stage.
• Onset of fingers sideway growth is when sharpest increase in population growth occurs.

In order to include viscous instability in modeling heavy oil waterflooding, it is essential to predict the nature of viscous instability. It is still unclear as to whether previous findings of viscous fingering in immiscible displacements in the presence of high single-phase permeabilities and linear displacement schemes are valid in displacement schemes similar to oil-field patterns (e.g., five-spot) and what the effect of dispersion (caused by varying velocity profiles) is on viscous fingering. To overcome the limitations of previous studies of viscous fingering in immiscible displacements, we conduct experiments in low-permeability, one-quarter five-spot patterns. The correlation of experimentally measured oil recoveries, pressure drops, saturation profiles, viscous fingers length and width, dynamic population of fingers, and rate of growth of fingers population with time and front position are discussed. Study of viscous fingering patterns in heavy oil waterflooding conducted in this work provides new insights into the onset of fingering and fingers development.