Characteristics and impact of asphaltene precipitation during CO2 injection are investigated for a Middle East crude oil in both sandstone and carbonate cores through phase behavior studies, corefloods and analyses of the deposition process using a compositional simulator. In phase behavior studies, a light-scattering technique with near infrared was used to determine the onset pressure of asphaltene precipitation. Also investigated were the effects of CO2 concentration on precipitation, including the potential for precipitation by CO2 at the current reservoir pressure.
The coreflood tests were conducted above the minimum miscibility pressure (MMP) in both carbonate and sandstone cores to investigate any difference in asphaltene precipitation characteristics in them. The asphaltene content in the produced oil decreased after the CO2 breakthrough –- an indication of its precipitation within the core. A careful post-test analysis of the flooded cores revealed that a larger amount of asphaltene was left behind in carbonate cores than sandstone core.
A compositional simulation study with tuned EoS parameters was carried out to evaluate coreflood results, followed by a parametric sensitivity analysis. In addition, the effects of rock heterogeneities on the oil recovery and asphaltene precipitation were investigated. A good match with the oil recovery was obtained. Results indicate that higher the degree of heterogeneities, the higher is the asphaltene accumulation in the core.