Paraffin and asphaltene problems can significantly reduce well profitability, causing troublesome operational issues, damaging formations, and decreasing production. Although often mentioned together, paraffin and asphaltene are distinctly different in their composition and behavior and different remediation solutions are required. In comparison, asphaltene deposition and removal is much more problematic than paraffin deposition and removal. The most common asphaltene removal techniques use xylene or xylene mixtures, which typically have limited effectiveness in addition to undesirable health, safety, and environmental characteristics.
This paper describes laboratory investigation of alternative solvent systems for removal of asphaltene deposits. Theoretical solvency parameter comparison based upon methods developed by Hildebrand and Hansen allowed solvents and cosolvents to be screened. The problem of formation wettability was addressed through the use of water-wetting surfactants. Finally, it was discovered that the primary solvent and cosolvent(s) could be dispersed in water yielding a water/aromatic solvent mixture that would not only effectively dissolve and disperse asphaltene, but also leave the formation in a water-wet state to delay production decline.
The new water-based asphaltene removal system was first applied in southern Europe in 2005. Since then, the system has been optimized for broader global operations whilst maintaining the favorable HS&E characteristics of the initial development. The system is unique as it provides a high-flashpoint water/solvent mixture with solvency power often greater than xylene and the additional benefit of leaving the formation strongly water-wet.
Problems associated with asphaltene and paraffin deposition have been identified in petroleum literature for over 70 years. Although often mentioned together, paraffin and asphaltene are distinctly different in composition and behavior. As a result, different remediation solutions are required. Paraffins are composed of straight-chain hydrocarbons generally accepted to be C18–20 up to C70 or higher.
Paraffins may also contain a variety of branched alkyl or saturated cyclic groups. Asphaltenes are heterocyclic unsaturated macromolecules consisting primarily of carbon, hydrogen, and minor components such as sulfur, oxygen, nitrogen, and various heavy metals. These higher-molecular-weight components of crude oil are in equilibrium under normal reservoir conditions. As crude oil is produced, this equilibrium may be upset by a number of factors leading to asphaltene deposition.
Asphaltene deposition can occur anywhere in the production life cycle: in the formation, in the near-wellbore region including perforations, in the tubing, downhole and surface chokes, surface flow lines, and separation equipment. Predicting where asphaltene deposition might occur requires an understanding of the mechanisms for asphaltene deposition. The key causes are pressure decrease and the introduction of incompatible fluids (Newberry and Barker 2000).