CO2-EOR Primer: https://www.netl.doe.gov/file%20library/research/oil-gas/CO2_EOR_Primer.pdf
Pretty good summary. I have been involved with EOR projects including CO2 floods for decades.
When one reads it, one has to be asking why more oil is not undergoing Enhanced Recovery using CO2?
It after all is proven to work but is not generally applied save in specific places in the industry.
1. It is expensive. Adds a few bucks per bbl produced.
2. One needs CO2. Seems obvious, but a source of CO2 is extremely important. The only large-scale floods such as out in West Texas have large quantities of sourced CO2 available, mostly in Colorado. Gas plants invariably emit CO2 but that needs to be captured and pipelined to a nearby suitable field.
3. It is corrosive. Yeah, CO2 in the presence of water greatly increases the corrosion of produced fluids. More $/b to handle.
4. One needs miscibility to get best economics. So most oil fields do not qualify as candidates. See
Criteria for Screening Reservoirs for CO2
EOR Suitability
Depth, ft < 9,800 and >2,000
Temperature, °F <250, but not critical
Pressure, psia >1,200 to 1,500
Permeability, md >1 to 5
Oil gravity, °API >27 to 30
Viscosity, cp ≤10 to 12
Residual oil saturation after
waterflood, fraction of pore space >0.25 to 0.30A couple of more bullets:
a. It is my belief that most papers overestimate the amount of recovery of oil via CO2. Why? Because implementing a CO2 flood entails drilling a lot more infill wells, maybe 2X as much, to achieve the proper reservoir sweep. An infill well will recover some oil without the help of CO2, but ALL of its production will be included anyway as incremental CO2 recovery.
b. Other fluids can produce the same effect as CO2 under miscibility. NGLs is a good one, but is expensive to purchase and use and is normally rejected for that reason. Nitrogen is abundant and cheap, but its miscibility pressures are high and need the right type of reservoir.
c. The types of reservoirs currently being drilled (shales, unconventionals) do not lend themselves to the usage of CO2 as their permeability is too low. There are test cases out there still as the IP volumes are so great it is tempting to try.
