Asphaltene precipitation studies : modeling, validation, and prevention

Abstract

Asphaltene precipitation and deposition caused by changes in composition, pressure, and temperature during oil production have a huge economic impact in the oil industry because of production losses and high remediation costs. To better understand and better predict asphaltene precipitation, different models for asphaltene precipitation were investigated and a thermodynamic model has been developed to predict asphaltene precipitation onset conditions from ambient titration data. The model predictions were validated using high pressure-high temperature titrations and pressure depletion experiments. When asphaltene precipitation can not be avoided during oil production, asphaltene dispersants are used to prevent asphaltenes from flocculating into large particles and depositing onto the pipe wall. Asphaltene dispersants were investigated using a variety of measurement technique (automated flocculation titrimeter, optical microscope, turbidity measurement device, and particle size distribution measurement device). The results show that asphaltenes in stable crude oil are nanoaggregates (less than 20 nm). However, when destabilized, these nanoaggregates agglomerate and form large particles of the size greater than l micron, which can settle and deposit. Asphaltene dispersants can stabilize asphaltense by preventing them from growing larger than l micron and thus delay the settling.