Evaluation of solvents for in-situ asphaltene deposition remediation

Upon the formation and the accumulation of the deposits, cost-effective cleaning strategies should be applied to remediate and remove the organic solids. The injection of aromatic solvents, usually know as solvent wash, is one of the commonly used techniques to re-dissolve the deposited asphaltenes in the well. To select and develop the best solvents and the most appropriate solvent soaking conditions for asphaltene remediation, a re-dissolution test apparatus using a packed bed column was introduced to evaluate the solvents for in-situ asphaltene deposition remediation under more realistic production conditions. The solvency power of three aromatic solvents and four commercial solvents was determined and compared. Under the current experimental conditions, the injection of p-xylene re-dissolves 31.3% and 69.8% more deposits than the same volume of toluene and aromatic naphtha (A150). Additionally, the solvent wash by toluene/diesel mixture (50/50 by volume) and diesel significantly reduces the re-dissolution efficiency by 31.1% and 74.3% by comparing to toluene. Results also suggest that the screening of chemical solvents based on their solubility parameters may not provide accurate indication on the selection of the best solvent for asphaltene removal. Furthermore, the effects of aging time, occluded oil, soaking temperature, and soaking time were investigated on the removal of asphaltene deposition in the packed bed column. Results show that the existence of the occluded oil during the aging and soaking process weakens the solubility power of the toluene. The solvency power of toluene is enhanced by 11.4% and 24.2% when the soaking temperature increases from 25 degrees C to 120 degrees C and the soaking time extends from 1 h to 24 h, respectively. With the proposed technique to assess chemical solvents in the laboratory, the most cost-effective solvent wash strategy can be developed for the in-situ remediation of asphaltene deposition in the wellbore.