Blending
of different crude oils is currently carried out in the
petroleum industry. However, under certain process conditions, i.e.,
pressure, temperature, flow regime, composition, etc., asphaltene
precipitation and plugging of pipelines and process equipment commonly
occur, which cause production shutdowns; therefore, special cleaning
programs need to be developed. To avoid these problems, it is first
necessary to evaluate the compatibility of crude oil blends through
a study of asphaltene stability. Most of the available tests are focused
on analyzing crude oils under standard conditions, i.e., temperature,
pressure, solvent/oil ratio, or static testing; however, studies at
dynamic conditions are scarce. Dynamic testing is a more representative
approach to correlate experimental information with data of transportation
of crude oils, where pressure, temperature, and flow regimes influence
crude oil stability and compatibility. In this work, the literature
reports of dynamic experimental setups are summarized and analyzed,
whereby asphaltene deposition and precipitation are typically studied.
Appropriate prediction of asphaltene
stability can anticipate operational
problems such as plugging of lines and process equipment (pumps, heat
exchangers, separation tanks, among others), thus assuring the production,
processing, transportation, and storage of petroleum. In the present
study, the physical and chemical properties of a series of Mexican
crude oils with American Petroleum Institute (API) gravity ranging
from 10 to 52 were determined. Based on saturate, aromatic, resin
and asphaltene (SARA) analysis, the following indexes were calculated:
colloidal instability index, colloidal stability index, Stankiewicz
stability criterion, stability cross plot, and oil compatibility model.
The stability of crude oils was also evaluated by means of experimental
techniques such as spot test, S-value, and static
stability test column. No uniform results were obtained when determining
the stability of crude oils with different methodologies. Due to the
discrepancies disclosed, it is recommended to evaluate stability by
various methodologies to adequately predict the stability of asphaltenes
in crude oils. Hence, the stability of asphaltenes in a given crude oil may be ascribed based on the average
result. However, from a practical point of view, pertinent cautions
on the handling of samples must be observed if at least one of the
methods classifies the sample as unstable or metastable.
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