(165e) Modeling Asphaltene Precipitation in Crude Oil Systems

The insolubility of asphaltenes in light paraffin liquids and other incompatible fluids, such as carbon dioxide (CO2), is a source of problems during crude oil production operations. Asphaltene precipitation can cause formation damage and wellbore plugging, requiring expensive treatment and cleanup procedures. In the presence of light gases such methane, ethane, propane and nitrogen (N2), asphaltenes are usually more stable as pressure and temperature increase; however, experimental measurements indicate that in the presence of CO2, asphaltenes become more stable as temperature decreases.

In this work, asphaltene phase behavior in a live reservoir fluid and a dead oil from South America is investigated in a range of pressures and temperatures in presence the of CO2 using the Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) equation of state (EOS). This thermodynamic model has been applied to asphaltene precipitation with different crude oil systems, such as those that involve methane, ethane or N2. Simulation results using the PC-SAFT EOS model are in good agreement with experimental measurements. A thermodynamic analysis using a model live oil confirms and explains a crossover behavior observed in the simulation of the precipitation onset with CO2. Simulations show that CO2 can act as an inhibitor or a promoter of asphaltene precipitation depending on the range of temperature, pressure and composition studied. At fixed pressure and live oil composition, CO2 addition increases the asphaltene stability below the crossover temperature, whereas above this point the asphaltene is less stable for increasing CO2 concentration.