Flocculation Onset Titration of Petroleum Asphaltenes

Abstract

The abundantly used technique of flocculation onset titration (FT) of asphaltenes is investigated, and it is shown how additional information on asphaltene and oil properties in terms of solubility parameters may be derived from the data obtained. The classical ways of interpreting the results are outlined. Analysis of the effect of oil concentration on FT is shown to add information on the stability of the asphaltenes in the oil. Application to various areas of asphaltene stability related problems is shown. This includes emulsion stability by asphaltenes, change in stability by conversion, oil field deposition, segregation, and asphaltene dispersant evaluation. Recommendations are given on the performance of this type of experiment, such as on titration rates. The analyses of more than 25 different oils are reported in the present work.

A Shortcut Application of a Flory‐Like Model to Asphaltene Precipitation

“…The measurement of flocculation onset is used; it consists of the gradual addition of a precipitant (n-heptane in most cases) to the crude oil and the determination of the minimum volume needed to provoke a phase-split. [13] The onset is usually detected by a change in one of the following properties: UV-VIS absorbance; NIRabsorbance; electrical impedance; electrical resistance; refractive index. [14] Stock tank oil samples are preferred because representative live oil samples are hard to obtain and prohibitively expensive.…”

Temperature effects on solubility of asphaltenes in crude oils

“…Andersen (1999) also used true boiling point distillation to concentrate asphaltenes in crude oil for asphaltenes A c c e p t e d M a n u s c r i p t flocculation studies. The test samples for the AFT experiments were prepared at three successively increasing concentrations (in the range of 0.5 -0.9 g/ml) in 30 ml test reaction vials.…”

“…The typical value of P lies from 2.5 to 10. The oils having a P value lower than 2.5 are considered to be less stable and those having a value above 2.5 are designated to be more stable (Andersen, 1999;Heithaus, 1960). The overall stability parameter P is expressed as:…”

“…Empirically, it is estimated as (Andersen, 1999;Laux, 1992): (12) The increasing trend of asphaltenes solubility parameter as a function of temperature can be seen in Fig. 12.…”

A Comprehensive Solubility Model for Asphaltene-Flocculation Prediction at Field Conditions

“…Figures 18 and 19 show that the mixing of miscible injectant in the live oil lowers the live oil solubility parameter. 6 On the other hand, slightly more than 30 mole% of the miscible injectant added to the live crude oil B1 caused asphaltenes to flocculate.…”