Modeling Study of CO2-Induced Asphaltene Precipitation†

Abstract

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 the temperature decreases. In this work, the 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 the presence 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 upon 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 becomes less stable when the CO2 concentration is increased.

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