An Evaluation of New Aspaltene Inhibitors; Laboratory Study and Field Testing

Abstract

Three candidate asphaltene inhibitors have been laboratory tested for their effectiveness on a Canadian crude. One inhibitor, an oil-soluble polymeric dispersant developed by Shell Chemicals, showed superior behaviour compared to the others: flocculation titrations with n-heptane resulted in an optimum concentration of 1300 ppm. PVT calculations, however, indicated that the prevailing conditions downhole can be quite favourable with respect to the amount of effective inhibitor compared to the atmospheric laboratory titrations which appear to be quite severe tests. Therefore, lower initial concentrations were recommended for a field trial. The chemical could be continuously injected through a capillary string, thereby avoiding the lost oil production associated with solvent cleaning operations. It has proved to be very effective at concentrations as low as 66 ppm, resulting in both a technically and an economically successful trial. Introduction Precipitation of asphaltenes in reservoirs, wells and facilities has a severe detrimental impact on the economics of oil production because of a reduction well productivity and/or clogging of the production facilities. The nature and behaviour of asphaltenes in crude oils is complex. Asphaltenes are heterocyclic macromolecules mainly consisting of carbon and hydrogen and minor components such as sulphur, nitrogen, and oxygen. It is generally accepted that resins and maltenes (these structures are comparable to asphaltenes but with a much lower molecular weight) are responsible for keeping the asphaltene particles in dispersion. The asphaltenes are surrounded by the polar head groups of the resins and maltenes while the nonpolar alkyl tails interact with the oil phase. So, crudes with a high ratio of resins to asphaltenes are less subject to asphaltene deposition whereas crudes with large amounts of non-polar saturates compared to aromatics are more prone to exhibit asphaltene precipitation problems. At "normal" reservoir conditions the asphaltenes, resins, maltenes and oil phase are in thermodynamic equilibrium. This equilibrium can be disturbed by a number of factors: decline of the reservoir pressure towards the bubble point, change in temperature or addition of a miscible solvent to the oil as applied in various EOR techniques. Much research has been focused on modelling the deposition behaviour of asphaltenes in reservoir crudes upon changes in pressure, temperature or composition. These models are based on the Flory-Huggins theory for colloidal systems and calculate the chemical potential for large molecules in the various phases. They require solubility parameters as input. In addition, the industry has made a substantial effort to develop pragmatic solutions to the problem of asphaltene deposition in producing wells.

Ready for Gas Injection: Asphaltene Risk Evaluation by Mathematical Modeling of Asphaltene-Precipitation Envelope (APE) With Integration of All Laboratory Deliverables

“…However, the chemical-inhibitor squeezing treatment was stopped because it could not achieve adequate adsorption of squeezed inhibitor on carbonate-rock surface (i.e., its period of effectiveness was shorter than expected). For the time being, more conventional ways of continuous downhole inhibitor injection (Bouts et al 1995;Jackson 2007;Srivastava et al 1999) would not be considered in our case because of its large investment for the workover to introduce macaroni injection lines into dualcompleted wells. In spite of these various efforts and long histories, the asphaltene problem has not been remedied yet, and it was therefore decided to improve the fundamental understanding of asphaltene-precipitation behavior by integrating a comprehensive interpretation of all available laboratory data and fi eld records.…”

Investigation of Asphaltene Precipitation onset Conditions for Kuwaiti Reservoirs

“…The asphaltene molecules are surrounded by the polar heads of the resins and maltenes, while the nonpolar alkyl ends interact with the oil phase. Therefore, crudes with a high ratio of resins to asphaltenes are less subject to asphaltene deposition than crudes with large amounts of nonpolar saturates compared with aromatics, which are more prone to exhibit asphaltene-precipitation problems 5 . At normal reservoir conditions, the asphaltenes, resins, maltenes, and oil phase are in thermodynamic equilibrium.…”

Possible Use of Bacteria/Steam to Treat Asphaltene Deposition in Carbonate Rocks

“…Chemical methods are the most popular ones for asphaltene treatment since they can be used to treat depositions in wellbore and/or into the producing formations. Chemical treatment falls into three major classes 8,9,10,11,12,13 : (a) Solvent treatment: Solvents (such as toluene and xylene) are used generally to dissolve deposits of asphaltene, (b) Asphaltene detergents: detergents are a class of surfaceactive agents. They are used to break up the asphaltene deposits and also prevent them from re-agglomerating back, (c) Crystal Modifiere: They are polymers 14,15 used to alter wax crystal growth by disrupting nucleation, crystallization, or modification of the paraffin crystals.…”