화학공학소재연구정보센터
Energy & Fuels, Vol.35, No.1, 329-340, 2021
Uneven Distribution of Asphaltene Deposits in CO2 Flooding Path: Interpretation by Combining Thermodynamic and Micro-CT 3D Geological Porous Models
Postcore flood analysis was conducted on a tertiary-mode CO2 flooding test under reservoir conditions. A composite carbonate core was retrieved to extract remaining hydrocarbons via Dean-stark distillation, and asphaltenes were measured in the extracted oil from each plug core using the IP-143 method. The analysis revealed uneven variation of asphaltene mass along plug cores: more asphaltenes were collected from the inlet-side core. To understand the mechanism of uneven in situ asphaltene-deposition, two numerical models were adopted that were based on thermodynamic and three-dimensional geological porous transport. The outcomes of thermodynamic modeling, using a cubic-plus-association model to estimate asphaltene precipitation as a function of CO2 concentration, proposed a scenario causing the uneven asphaltene distribution by incorporating vaporizing-gas-drive (VGD) into an asphaltene-destabilizing mechanism. This means more asphaltene deposition was predominantly caused when purer CO2 was in contact with fresh reservoir oil. The vaporized intermediate hydrocarbons in front, extracted through VGD, might dilute the injected CO2 concentration in the gas phase. This briefly caused the CO2 concentration to be higher in the inlet-side cores and lower in the outlet-side cores. Using a micro-CT scanned core, a 3D geological transport model was generated to estimate in-depth penetration of asphaltene particles in porous media. Three particle sizes (0.59-17.6 mu m) were modeled as per visual inspection of destabilized asphaltene particles/aggregates that grew as oil was mixed with higher CO2 concentration (average particle diameters of 2.5, 3.6, and 17.6 mu m for 0, 20, and 40 mol % CO2 addition). The setting of model particle sizes also considered the pore throat size distribution of the 3D geological transport model. The 3D transport model results propose a subsequent scenario in which smaller asphaltene spheres penetrate more deeply in porous media.