GPC analysis of asphaltenes from steam stimulated oil wells

Gel permeation chromatography was used to obtain molecular weight distributions of asphaltenes from 5 wells before and after steam injection. These wells all produce from the same horizon in one Kern River, California, field. A standard Q-mode correlation analysis showed no significant relationship of stimulation response to any of the molecular weight data, e.e., molecular weight distribution before, immediately after, or 200 days after treatment. A standard R-mode analysis showed a significant relationship of the slope of the molecular weight curve before stimulation with the slope just after stimulation, but not with the slope 200 days after stimulation. The wells which returned the least amount of oil per barrel of water injected as steam produced asphaltenes after stimulation very deficient in high molecular weight compounds. It is inferred from this that these materials precipitated within the formation and are restricting flow. At the other extreme, the change in asphaltene molecular weight profile from the most successful stimulation job can best be explained by the introduction of new production sources into the oil flowing toward the well.