Mitigation and remediation of asphaltene precipitation, deposition and plug formation: Importance of asphaltene subfractions
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Asphaltenes represent the heaviest and most polar constituent of petroleum. They consist of a wide range of molecules differing in molecular weight and functional groups. Under reservoir conditions, the asphaltenes generally remain stabilized in crude oil, either in dissolved or colloidal form. However, changes in pressure, composition or temperature during crude oil production can lead to asphaltene precipitation and deposition in pipelines and facilities. The problem is further compounded by the observation that only a small fraction of asphaltenes are responsible for deposition challenges encountered in the industry. This thesis aims to identify these problematic asphaltene fractions, and find ways to mitigate/remedy the associated challenges. The first part of the thesis focuses on developing methods to fractionate asphaltenes, followed by physio-chemical characterization of the asphaltene sub-fractions obtained using a variety of experimental techniques. This procedure helps us to distinguish between the stable and unstable asphaltene fractions in crude oil, and provides information about structural differences between them. In the second part of thesis, different ways to mitigate/remedy asphaltene precipitation and deposition were explored. To begin with, the concept of Hansen Solubility Parameter (HSP) was utilized to identify the characteristics of desired solvent or solvent mixture for removal of asphaltene layers formed on the surface of stainless steel. Thereafter, chemical treatment method was investigated using a commercial inhibitor/dispersant. Here, the focus was to determine the mechanism of interaction between the asphaltenes (and sub-fractions) and inhibitor, and to find out how the commercial inhibitor prevents the formation of asphaltene layers or helps in removal of asphaltene layers from solid surfaces. The knowledge obtained from the work undertaken in this thesis can thus form the starting point for design of efficient chemicals to overcome asphaltene precipitation and deposition problems.