Carbon Dioxide Enhanced Oil Recovery ( CO2EOR)

Oil recovery is a term involves methods used for increasing the amount of crude oil that can be extracted from a petroleum reservoir.Recovery methods are classified as primary, secondary and tertiary.
Carbon dioxide ( CO2) flooding is a tertiary oil recovery method in which carbon dioxide is injected into an oil reservoir in order to increase the output while extracting crude oil.Injecting carbon dioxide into the pore spaces of a rock help move crude oil out as it has two characteristics that make it suitable for oil recovery: it is miscible with crude oiland less expensive than other miscible fluids.



  • When two or more fluids are mixedand no interface exists between themafter some amount of one fluid is added to others, they are termed as miscible.
  • But if two or more fluid phases form, the fluids are considered immiscible.

Production plot

Types of Carbon dioxide displacement:

Flooding a reservoir with CO2 can occur either miscibly or immiscibly.


  1. Miscible CO2 Displacement:
    Under suitable reservoir pressure at a depth generally greater than 1200m and oil gravityless than 22° API gravity, injected carbon dioxide will mix thoroughly with the oil within the reservoir such that the interfacial tension between these two fluids disappears. Oil recovery will be from 10 to 15% of OOIP (original oil in place).
    The minimum pressure at which miscibility between CO2 and crude oil can occur is called Minimum Miscibility Pressure (MMP). Low pressured reservoirs may need to be re-pressurized by injecting water.
  2. Immiscible CO2 Displacement:
    When reservoir pressure is too low and oil gravity too large, the injected CO2 will not mix with the oil and remains physically distinct within the reservoir. However, injected CO2 still can improve oil recovery by causing the oil to swell-oil’s volume to increase-, reducing its density and improve mobility. But this method is not efficient.
    The production plot shown below illustrates how a field can respond to CO2 injection. This example, for Shell Oil’s Denver Unit in the Wasson Field in West Texas, shows oil and water production, and water and CO2 injection, over sixty years.
Procedure of CO2 EOR:

field, and a meter measures the volumes of the gas purchased.
CO2 is injectedat its MMP or above into the reservoir using injection wells to free the trapped oil.
CO2 enters the reservoir, moves through the pore spaces of the rock and mixes with the crude oil miscibly reducing the viscosity of the trapped oil so that it flows more easily.
Water is injected in alternating cycles with CO2 to sweep the oil to the producing wells; the water may mix with the oil causing the recovered liquid to become mostly water which had to be separated from the oil.
Production wells pump the oil, CO2, produced water and any natural gas to the surface.
The CO2 and associated natural gas are separated, and then CO2 is recompressed for reinjection with additional newly-purchased amounts.



Oil graph CO2 injection
CO2 Pipeline Metering Gas compressor
Advantages:

CO2 Flooding is consideredto be the greenest way to recover oil as carbon dioxide frees the oil easily and affordably.After the oil has been recovered, the CO2 is trapped in the reservoirin a solution called "carbon capture and sequestration."


Disadvantages:

The high mobility of CO2 is a main problem in CO2 flooding. Also, the relative low density and viscosity of CO2 compared to reservoir oil causes gravity tonguing and viscous fingering – the interface of the two fluids does not remain flat but the less viscous fluid moves faster than the more viscous one deforming the interface and making fingered profile



Visicous Fingering