Explanation of Asphaltene Phase Behavior

Asphaltenes represents one of the major flow assurance challenges in upstream oil production. Asphaltene precipitation and deposition can occur at different stages of production causing reservoir formation damage and plugging of pipeline and production equipment. Asphaltenes are also a challenge in refining operations both in plugging of heat exchangers and contributing to coke formation in catalytic crackers. Part of the challenge is that asphaltenes represent a polydisperse distribution of molecules that are defined primarily by their solubility in certain solvents since their molecular structures are difficult to determine.

Predicting asphaltene flow assurance issues requires the ability to model phase behavior of asphaltenes as a function of temperature, pressure, and composition. In this presentation, we review some recent approaches to model asphaltene phase behavior. We also present a method to characterize crude oil including asphaltenes using the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT). The theory accurately predicts crude oil bubble point and density as well as asphaltene precipitation conditions. The theory is used to examine the effects of gas injection, oil based mud contamination, and asphaltene polydispersity on the phase behavior of asphaltenes. The analysis produces some interesting insights into field and laboratory observations of asphaltene phase behavior.