Abstract: ABSTRACT: An Experimental Approach to Prediction of Asphaltene Flocculation
Asphaltenes can cause problems in oilfield operations, oil transportation, and in petroleum refining operations; they have been the subject of extensive study. Many of the existing models that have been developed to predict the onset of asphaltene flocculation rely on approximations to a full thermodynamic treatment and on parameters that are not available except by fitting HTHP data to the model. A much simpler approach has been developed based on experimental measurements of refractive index (RI) at the onset of flocculation and calculation of RI at reservoir conditions. The onset of asphaltene flocculation is often observed in mixtures of oil, solvent, and asphaltene precipitants. The key to the proposed method is the use of direct measurements of RI to replace estimates of solubility parameters based on fitting an imposed model or on values obtained at infinite dilution of oil in mixtures of solvents and precipitants. RI is readily measured and is a good indicator of the ability of the oil to maintain a stable dispersion of asphaltenes. A common trend, observed for a wide range of crude oils, can be used to evaluate new oils from a minimal number of experiments that establish the RI at the onset of flocculation with heptane or other asphaltene precipitants. The method has been extensively tested with stock tank oils and their asphaltene fractions. Results obtained at ambient conditions for stock tank oil can be extended to reservoir conditions using standard PVT and compositional data.
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California