Investigation of the effect of injection gas compostion on CO2-rich flooding and its implications in an onshore Australia oilfield

Abstract

Results of a reservoir condition core flood were matched by a compositional model. Using this model as a base case, the effect of gas composition on oil recovery from an onshore Australian oil field was investigated. Based on this and earlier studies it was found that CO2 injection in this field gave MMP values well within proposed injection pressures. Even at concentrations of methane as high as 50% and CO2 of approximately 25%, oil recoveries remained only slightly under that of pure CO2 so long as significant quantities of C3+ were retained in the injection gas stream. This effect of the C3+ fraction was further investigated by isolating the effect of n-pentane in the injection gas on a 92 mol% CO2 and 8 mol% methane gas mix. It was found that while recoveries certainly improved, the economic gain from the extra recovery is likely to be outweighed by the cost of n-pentane.