Immiscible displacement in CO2 flooding

[exiledindian]

Hello,

Could anyone please explain in simple terms the phenomenon of immiscible displacement during CO2 injection in an oil reservoir? This is with respect to oil swelling and viscosity reduction, how does the exact process take place?

Many thanks.

[Sequestrator]

in simple terms, chemical reactions with some components in oil, and/or mixing occur after some pressure (miscibility pressure) is reached. At that point, you affect interfacial tension, density and viscosity of oil. If CO2 injection pressure is below minimum miscibility pressure, CO2 injection can be described with some method based on frontal advance theory (Buckley-Leverett) i.e. you can consider front of CO2 which is displacing front of oil.

In petroleum industry/science/technology, there are some terms that are confusing to me. You can find published CO2 - oil solubility correlations, and you can find minimum miscibility pressure research results. It seems that oil has too complex form/composition, and high pressure and temperatures allow both solubility and miscibility to be parameters that are crucial to injection of some fluid. However, I'd say, if physical forces (for example gravity) cannot significantly affect reservoir fluid and injected fluid - that is due to solubility. If the pressure is the most important parameter for breakthrough of injecting fluid, we can say that the only parameters that seem to obstruct moving of injecting fluid front are petrophysical - heterogeneity of relative permeability and pore structure.
Also, if front of injection fluid theoretically would be the same through some time, the fluid doesn't dissolve. The best are examples related to CO2 geological storage - part of CO2 will "disappear" in brine, so you can inject CO2 bellow miscibility pressure, but after injection, CO2 dissolves in brine, and new mixture would exist in aquifer.

[exiledindian]

Thank you Mr. Sequestrator for your detailed response. I have been doing a bit of background reading from research papers and EOR textbooks which has enhanced my knowledge about immiscible displacement. Its sure seems to increase oil recovery in reservoirs with pressures falling below the MMP even after waterflooding, especially for light oils.

However, immiscible CO2 flooding for heavy and medium oils has also been tried with mixed results. As we are talking in terms of solubility, CO2 is a more soluble in oil than either N2 or Methane (often used as substitutes) which can be expected for oils with a greater fraction of light and intermediate components. But for oils with a large C7+ fraction, obviously the recoveries are not as good. Have you come across N2 or CH4 giving good recoveries for heavy oils? It would be interesting to read some published results on such pilot projects.

in simple terms, chemical reactions with some components in oil, and/or mixing occur after some pressure (miscibility pressure) is reached. At that point, you affect interfacial tension, density and viscosity of oil. If CO2 injection pressure is below minimum miscibility pressure, CO2 injection can be described with some method based on frontal advance theory (Buckley-Leverett) i.e. you can consider front of CO2 which is displacing front of oil.

In petroleum industry/science/technology, there are some terms that are confusing to me. You can find published CO2 - oil solubility correlations, and you can find minimum miscibility pressure research results. It seems that oil has too complex form/composition, and high pressure and temperatures allow both solubility and miscibility to be parameters that are crucial to injection of some fluid. However, I'd say, if physical forces (for example gravity) cannot significantly affect reservoir fluid and injected fluid - that is due to solubility. If the pressure is the most important parameter for breakthrough of injecting fluid, we can say that the only parameters that seem to obstruct moving of injecting fluid front are petrophysical - heterogeneity of relative permeability and pore structure.
Also, if front of injection fluid theoretically would be the same through some time, the fluid doesn't dissolve. The best are examples related to CO2 geological storage - part of CO2 will "disappear" in brine, so you can inject CO2 bellow miscibility pressure, but after injection, CO2 dissolves in brine, and new mixture would exist in aquifer.

[Petrol4]

thank you

[Sequestrator]

Hi, I think that miscible process will be in most cases better option for EOR - CO2 will decrease molar weight i.e. density of oil, and its viscosity as well. If you experience immiscible conditions, than you can expect only the pressure increase benefit, but for mature oil fields, the goal is to improve oil mobility, not to increase the pressure.