(207c) Thermodynamic Validation of Asphaltene Phase Transition Phenomenon Using High Pressure Nir Cell

High asphaltene content associated with emerging prospects of the heavy oil reserves creates new challenges in production and processing of the crude oil caused by phase transition of asphaltenes. Changes in pressure, temperature and composition of the system during oil production and processing can result in thermodynamic transition of the miscible asphaltene phase to a separate solid phase. Formation of the asphaltene solid phase reduces the efficiency of equipments and reactors by plugging and fouling, which has a significant economic impact on the heavy oil production. In order to describe the phase transition of asphaltenes, an advanced thermodynamic model has been developed base on the theory of Gibbs free energy of mixing incorporating entropy of mixing assuming regular solution and enthalpy of mixing based on Hildebrand cohesive energy density concept. A high pressure cell with a laser near-infrared (NIR) detector system has been constructed to experimentally observe the phase transition and generate data to validate the model. This high pressure system is capable of performing a constant pressure titration of a live crude oil with normal alkanes or compressed hydrocarbon gases at a pressure up to 650 bar and a temperature up to 200°C. The experimental set-up can also be operated in a closed system mode performing pressure depletion of a live reservoir crude oil and observing asphaltene phase transition as a function of pressure. Several live crude oil systems with miscible compressed gases have been tested using this cell and the results showed an excellent agreement with the thermodynamic model. This model can be used to predict the phase transition of the asphaltenes at any condition during crude oil production and processing. These predictions can be used to either improve the design of the production and processing facilities to avoid the asphaltene phase transitions or develop an optimum remediation (chemical or mechanical) program for asphaltene control. This presentation will elaborate the formulation of the thermodynamic model, describe the operation of the high pressure experimental set-up, discuss the experimental data, and show the agreement between experimental and predicted results.