Effects of Stepdown Pressure and Wettability on Bubble Nucleation in Gas-Supersaturated Oil-Water Systems

This study investigates the influences of wettability and stepdown pressure on pressure-driven bubble nucleation within a gas-supersaturated oil-water system. Two gases—carbon dioxide (CO2), which is highly soluble in water, and methane (CH4), which is sparingly soluble in water—were used individually for the bubble nucleation experiments. Equal heights of oil (n-decane) and water, in a wettability-controlled glass vial placed in a saturation cell, were saturated with either of the gases at 6000-mbar pressure, followed by applying a stepdown pressure of either 6000 mbar, 500 mbar, or 100 mbar to start the bubble nucleation process. The average bubble nucleation pressures for CO2 and CH4 gases on a hydrophobic vial surface with 500-mbar stepdown pressure were 4333 ± 289 mbar and 3833 ± 289 mbar, respectively. It is important to note that the bubble nucleation took place exclusively on the portion of the solid surface submerged in water. However, bubble nucleation did not take place with 100-mbar stepdown pressure for either gas in the hydrophobic vial despite the pressure being brought down to atmospheric pressure. As expected, bubble nucleation did not take place in the hydrophilic vial for the gases despite the pressure being brought down to atmospheric pressure from the saturation pressure, regardless of the stepdown pressure. In addition, bubble nucleation did not take place in CO2-supersaturated water in the oil-wetted hydrophilic and hydrophobic vials, even at maximum supersaturation.