Potential to Enhance CO2 Flooding in Low Permeability Reservoirs by Alcohol and Surfactant As Co-Solvents

Six gas-soluble chemical modifiers were dissolved in pure CO2 to improve the ability to extract, and displace, crude oil from low-permeability reservoirs. It was found that the ability of the modifiers to enhance crude oil extraction using CO2 increased in the order: water, ethanol, TX100, TX100/ethanol, TX45, and TX45/ethanol. As to oil displacements, the best performing system was CO2/TX45/ethanol which generated a significantly greater oil-recovery factor (by 13.8%) than pure CO2, making it a good candidate to replace pure CO2, however, when displacing bypassed oil, the enhancement in oil recovery gained by using CO2/TX45/ethanol was reduced to 6.0% (during the primary soaking stage) and it also failed to remove the majority of the bypassed oil (with a low oil-recovery factor of 23.3%). The secondary huff-n-puff using CO2/TX45/ethanol was more effective than the previous soaking process (increasing the oil-recovery factor to 88.1%), while also generally outperforming the recovery achieved using pure CO2 (depending on pressure depletion).