Summary

Wax deposition is one of the most significant challenges for flow assurance. In a conventional pigging operation, a fully coated foam pig is regularly used to mitigate wax deposition. This work attempts to assess, qualitatively and quantitively, the wax removal process of the fully coated foam pig. The experimental results confirm that the wax removal process of the fully coated foam pig includes four phases; namely, the buildup phase, preplug phase, plug phase, and production phase. Moreover, the effects of coating hardness, wax layer thickness, and the shear strength of wax sample on the wax breaking force and the wax removal efficiency are investigated experimentally. It is found that the wax breaking force decreases and the wax removal efficiency increases when the coating hardness is increased. On the basis of the analysis of the experimental results and Buckingham's π theorem, a semitheoretical model is developed to predict the wax removal efficiency of the fully coated foam pig. Furthermore, a force analysis model is used to calculate the wax breaking force by taking the wax removal efficiency model into account. The average relative errors between the calculated and measured results for the wax removal efficiency and the wax breaking force of the fully coated foam pig with 65 Shore A hardness (HA) coating are 24.13 and 31.88%, respectively. Analogous wax removal models for foam pigs of different types can be developed with the research method proposed in this work. Therefore, this research method provides a general strategy for wax removal research in crude oil pigging.

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