Wax Precipitation in Three Chinese Reservoir Oils under Carbon Dioxide (CO2) Injection

The wax precipitation behavior in three Chinese reservoir oil samples Xinli, MuH, and Xinmin reservoir oils have been studied under CO 2 -injection conditions. The effects of the injected CO 2 concentration on the amount of wax precipitation from the three oils have been studied at the reservoir temperatures and pressures. Considerable wax precipitations have been detected as the injected CO 2 concentration exceeds 50 mol %, and the amount of wax precipitation increases with the injected CO 2 concentration. The hydrocarbons extracted into the vapor phase during the multiple-contact extraction process using CO 2 have been observed to be mainly limited to C 1 −C 5 . The onset temperatures of wax precipitations from the CO 2 -saturated Xinli reservoir oil and the Xinli reservoir oil have been detected using a solid detection system (SDS) logging system at the reservoir pressure. The results show that the onset temperature of the Xinli reservoir oil is decreased as the saturation of CO 2 at the reservoir pressure increases. These results, together with those of multiple-contact extraction experiments, suggest that the wax precipitation under CO 2 injection may be caused by the extraction of light hydrocarbons from the reservoir oils.