Asphaltenes

Asphaltenes are a natural constituent of many crude oils and may be precipitated in production systems when the crude’s natural solvency for them is reduced. Several factors including, pressure, temperature, and composition can change the stability of these high molecular weight, polar molecules allowing them to flocculate.

 

Asphaltene deposition can be observed during normal operations at pressures above the bubble point. Alternatively, operations such as miscible gas injection or artificial lift can increase the risk of deposition.

 

KAT offers both the ASTM D4740 Spot Test and the Microscopy Titration technique initially developed by New Mexico Tech and Chevron as simple tools to assess the kinetics of asphaltene deposition in “dead” fluids and screen for potential asphaltene instability.

 

In the KAT dispersency test, asphaltenes in “dead” fluids are destabilised by addition of an alkane solvent at ambient pressure. Flocculated asphaltenes then sink towards the bottom of a graduated tube and form a sediment. The sedimented volume is the test measurement. Additives may inhibit flocculation or, more usually, retain the floccs in suspension [dispersion].

 

In conjunction with our partners, KAT can offer Asphaltene Onset Pressure determination using pressurised, bottomhole field samples. Alternatively, we can also offer ASphaltne InStability Trend [ASIST] modelling which estimates asphaltene instability in produced oil at various pressures and temperatures based on small volume, stock tank fluid measurements.

 

KAT and AFS have also collaborated with a major operator to develop an asphaltene deposition model, which can be used to assess whether destabilized asphaltenes will precipitate along the production stream. The advantage of these assessments is that they assess deposition rather than forced flocculation, which is a more critical parameter in flow assurance risk assessments.