CO2 miscible flooding was first successfully tested in North Dakota by Gulf Oil Company (Gulf) in 1981 at Little Knife North field. (1)(2)(3) Gulf achieved CO2 miscible oil recovery of 13% of the original oil in place (OOIP) on a 5-acre mini-test pilot. Gulf concluded based upon simulation forecasts that 160-acre development on a 5 spot pattern would recover up to 8% of the OOIP from CO2 miscible flooding. CO2 miscible flooding in North Dakota has never been demonstrated on a large-scale spacing pattern. Recovery of 8% of the OOIP is a widely accepted empirical value for carbonate reservoirs in the Permian basin but on a significantly smaller well spacing. Reservoir characteristics of successful Permian carbonate CO2 miscible floods are discussed in detail later in this report and show that average well spacing in successful Permian Basin CO2 miscible flooding projects is less than 40-acres per well to achieve recovery of 8% of the OOIP.
It is the authors’ opinion that 8% recovery of the OOIP on 80-acre well spacing in North Dakota is a more realistic estimate. Also it is the authors’ opinion that if CO2 flooding in North Dakota reservoirs is attempted on 160 acre wells spacing that significantly less than 8% of the OOIP predicted by Gulf would result due to reduced CO2 sweep efficiency as a result of porosity and permeability heterogeneity.