Modeling of asphaltene precipitation and deposition tendency using the PC-SAFT equation of state
Gonzalez Rodriguez, Doris Lucia
Chapman, Walter G.; Hirasaki, George J.
Doctor of Philosophy
Asphaltene precipitation and deposition can occur at different stages during petroleum production causing reservoir formation damage and plugging of pipeline and production equipment. Even though asphaltene deposition is a serious production hazard, deposition appears to occur only if precipitation is present. The main motivation of this work is to develop a general model for asphaltene precipitation and to understand the contribution of the surface material to asphaltene deposition. This dissertation presents a study of the effects of temperature, pressure, and composition on asphaltene phase separation prediction using the Statistical Associating Fluid Theory (SAFT) equation of state (EOS) and application of the theory to field cases. Furthermore, a molecular theory is used to predict the deposition tendency of asphaltene. Practical understanding of asphaltene precipitation applied to the oil field production is presented in this research project. A challenge overcame in this study was to translate this methodology to industrial application; initially, through the validation of the PC-SAFT EOS model as implemented in commercial computer software. Then, this work shows how SAFT qualitatively predicts different scenarios as actually occur in the field, i.e., the effect of gas injection, specifically, CO2, N2 and normal alkanes; oil based mud contamination and commingling of different live oil streams. These aspects were studied using crude oils from Deepwater Gulf of Mexico and Middle East. Finally, the impact of asphaltene precipitation considerations in a deepwater development project was studied based on experimental measurements of a hydrocarbon fluid when contacted with gas condensate from another zone. The evaluation was performed using multiphase thermal-hydraulic behavior coupled with the asphaltene PC-SAFT thermodynamic model. The PC-SAFT EOS adequately predicts the onset of asphaltene precipitation in all these cases. Simulation results agree with previous experimental reported work. On the depositional aspect a theoretical evaluation of the asphaltene adsorption behavior onto solid surfaces has been made to look for a relationship between the composition of the solution phase and the surface through the application of molecular theory. The asphaltene deposition tendency can be qualitatively described through the conventional Hamaker constant, which represents molecular van der Waals interactions between macroscopic bodies. Results show agreement with experimental observations.
Chemical engineering; Petroleum engineering