Mitigation of asphaltics deposition during CO2 ̄ood by enhancing CO2 solvency with chemical modi®ers

CO2 injected in the reservoir of McElroy Field, TX, for a CO2 ̄ood was in the supercritical state. Supercritical CO2 ̄uid is capable of extracting light and intermediate hydrocarbons from rocks but is unable to extract heavy hydrocarbons and asphaltics. Therefore, plugging of asphaltics in reservoir rocks and a consequent reduction in injectivity and recovery may result when CO2 only is used in enhanced oil recovery. By adding common solvents as chemical modi®ers, the ̄ooding ̄uid shows marked improvement in solvency for heavy components of crudes due to its increased density and polarity. Numerous supercritical CO2 ̄uid extractions of dolomite rock from the Grayburg Formation containing known amount of spiked McElroy crude oil have been carried out to evaluate extraction eciencies of CO2 and CO2 with chemical modi®ers at various temperatures and pressures. All experiments show that extraction eciency increases with increasing CO2 pressure but decreases with increasing temperature. Addition of chemical modi®ers to CO2 also shows improved extraction eciency and reduced asphaltic deposits. Under the pressure and temperature similar to McElroy reservoir conditions; chemically modi®ed CO2 yielded almost 3 times as much oil extracts as those in extractions with CO2 only. It also reduced the asphaltics content in extracted rocks to nearly one half; indicating its potential for mitigating asphaltics plugging of formation rocks # 2000 Elsevier Science Ltd. All rights reserved.