Page 277 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

248 Rouzbeh G. Moghanloo et al.

1958, Hirschberg et al., 1982). This important concept provides better
insight into its precipitation and deposition. The complex compatibility
between maletenes and asphaltenes also needs to carefully considered, as
they are intimately related to the stability of crude oil, and asphaltene
onset, precipitation, and deposition (Bearsley et al., 2004).
Asphaltene precipitation refers to the process when asphaltenes
become a separate phase from the crude oil. They remain suspended in
the liquid phase where the quantity and the size of the asphaltenes are rel-
atively small. Thereafter, the precipitated asphaltenes clump together
(aggregation) and form larger particles, also called flocs. The asphaltene
aggregates are initially suspended in the crude oil (Alian et al., 2011;
Moghanloo et al., 2015). Furthermore, the process of deposition follows,
the process whereby flocs attach to and accumulate on various surfaces.

6.2.1 Asphaltene precipitation
The factors which affect asphaltene precipitation are pressure, tempera-
ture, and crude oil composition
• Pressure:
The influence of this factor comes into play at values above the
bubble point. The Hassi Messaoud Algerian Field exemplifies this. In
that field, asphaltene deposits were found on the production tubing
because the wellhead pressure was near the crude oil saturation pres-
sure, where the precipitation reaches as maximum (Seifried, 2016). If
pressures remain above the bubble point, asphaltene solubility appears
to decrease with decreasing pressure, reaching its minimum at the
bubble point pressure. The solubility however increases with decreas-
ing pressure below the bubble point Burke et al. (1990).
• Temperature:
Temperature has been identified as a factor for precipitation, how-
ever, it’s effects have not been well understood. The change in asphal-
tene solubility with a change in temperature depends on the reservoir
temperature (Leontaritis, 1996), where the solubility increases with
temperature as long as it remains below the reservoir temperature.
When above the reservoir temperature however, the solubility
decreases with an increase in temperature.
• Crude oil composition:
Research shows that asphaltene solubility decreases as the amount
of gas in solution increases Burke et al. (1990).