In a CO2 miscible displacement process, the injected CO2 solvent can induce flocculation and deposition of asphaltenes and other heavy organic particles. This can cause numerous production problems with a detrimental effect on oil recovery. Therefore, it is important to understand the behavior of this organic matter under reservoir operating conditions. This paper presents results of dynamic and static precipitation tests conducted at reservoir temperature and pressure conditions to investigate the likelihood of asphaltene deposition problems in the Weyburn reservoir (in southeast Saskatchewan). A laboratory study using a high-pressure PVT cell was undertaken to determine the effect on asphaltene flocculation/precipitation of operating pressure, CO2 concentration, gas contaminants in CO2, and presence of formation brine for three different oil samples collected from the reservoir. The extent of asphaltene deposition was also assessed through coreflood experiments using preserved and restored reservoir core material collected from different reservoir zones of increasing permeability (Marly, Vuggy, and high-grain-size Vuggy) and through a suitably designed X-ray CAT-scanning visualization experiment.

Static tests indicated the most important factor on which the asphaltene precipitation depended was the CO2 concentration. For oils belonging to the same pool, the increase in asphaltene precipitation with solvent concentration was proportional to the initial asphaltene contents of the oil. Coreflood experiments showed a considerable increase in asphaltene deposition in the core matrix following CO2 injection. Pore topography of the core matrix played an important role in the extent of CO2-induced asphaltene deposition. The deposition appeared to be higher in a high-grain-size Vuggy matrix than in the normal Vuggy matrix, and lowest in the Marly matrix. X-ray CAT-scanning tests depicted localized areas of asphaltene deposition along the length of the core, with significant deposition suspected to be occurring near the inlet of the core. The CAT-scan tests also identified sites of suspected formation damage to the core matrix associated with CO2 injection.

You can access this article if you purchase or spend a download.