In a miscible displacement during enhanced oil recovery, what phenomenon causes irregular, finger-like patterns in the displacement front?

• A. Coning
• B. Channeling
• C. Fingering
• D. Spreading

Answer: (C)

Viscous fingering is the phenomenon at work here. When a displacing fluid with a lower viscosity pushes into oil (or a more viscous fluid) in a porous medium, the interface becomes unstable because the less-viscous fluid cuts into the more viscous one, rather than advancing as a smooth front. In miscible displacement, capillary effects are small, so the instability is dominated by this viscosity contrast. The result is irregular, finger-like channels that propagate ahead of the main front, creating the characteristic fingering pattern. Other terms describe different flow behaviors—gravity-driven coning, flow through high-permeability channels, or broad spreading—but they don’t produce the distinctive finger-like displacement front seen in viscous fingering.