ENHANCED OIL RECOVERY
NITROGEN FOAM FLOODING
As to nitrogen foam flooding, foaming agent and nitrogen gas are simultaneously injected into the stratum, and their combined action emulsifies the crude oil by reducing the oil water interfacial tension and changing the surficial wetting property of oil-wet rock, reduces the viscosity fingering phenomena, and implements uniform flooding.
Mechanism of N2:
• Keeping stratum pressure and replenishing stratum energy
• Beneficial to bring into play the oil flooding function of gas expansion
• Enable the agent to enter into some low-permeability oil-bearing pore channels water can hardly get in
• Redistribute the oil, gas and water
Mechnism of foaming agent:
• Change the rock surface wettability, and reduce the oil water interfacial tension to a great extent
• Foam flow requires a relatively high pressure gradient to overcome the rockpore capillary force and sweep the crude oil out of the fine pores
• The effect of "Defoaming when exposed to oil, and stabilizing when exposed to water" and "Step water instead of oil" can improve the oil flooding efficiency
• Since its viscosity gets high in high-permeability layer and gets low in low-permeability layer, the foam can play the role of 'stop the big instead of the small'
Swept area increased by foam flooding