Asphaltene Stability Prediction Based on Dead Oil Properties: Experimental Evaluation

The asphaltene content effect on crude oil properties was investigated for a series of deepwater Gulf of Mexico (GOM) fluids with asphaltene contents varying from 4 to 15 wt %. The objective of the study was to conduct flow assurance screening tests on GOM samples collected from different sands and determine properties of the dead oil and the asphaltene stability. Densities, refractive indices, and viscosities were measured at different temperatures in dead oils with three different asphaltene contents. The properties showed defined tendencies with the asphaltene content and with the temperature. The application of the one-third rule in the calculation of properties, such as solubility parameter and viscosity of dead oil systems, was evaluated. This approach also provides an alternative to calculate the refractive index based on densities obtained from an equation of state. The analysis also shows the important role that the asphaltene content plays in determining the viscosity of crude oil and evaluates the possibility of predicting viscosity from refractive index, as proposed by Vargas et al. Another important aspect to evaluate is the prediction of the asphaltene stability in the crude oil by measuring basic dead oil properties, such as density and refractive index. The asphaltene instability trend (ASIST) method was used to predict the asphaltene precipitation onset at reservoir conditions. In this analysis, the asphaltene stability was studied on the heaviest and lightest samples (high and low asphaltene content) by determining the minimum quantity of precipitant required to initiate asphaltene flocculation, followed by measurement of the refractive index of the mixture at the onset conditions. The asphaltene precipitation kinetic effect was also considered in this study.