Treatment of well flow lines with thermochemical/exothermic fluid has shown good results for wax removal compared to conventional hot oil, hot water or solvent treatments. However, the technique has not gained widespread use due to lack sufficient scientific publications that can give more insights over its use and help in designing a safe and effective treatment.
This paper presents a novel transient mathematical model for design and analysis of thermochemical treatment for well flow lines by taking into account the chemical kinetics, heat transfer, fusion of wax and associated two-phase flow. The governing equations have been solved using tools of computational fluid dynamics and heat transfer (CFD - HT). The resulting simulator can be used to prepare an optimum thermochemical plan by analysing the effects of important factors including wax details, deposition profile, heat loss, formulation composition and injection strategy.
Simulation results with the developed model indicate that entire filling of flowline with thermochemical fluid is not necessary for complete wax removal. Injection of a small thermochemical spacer in the flow line followed by its displacement with crude oil can be suffice in case of short flowlines of onshore fields. Selection of initial reactant concentration and pH has to be done judiciously based on the maximum allowed temperature in the flowline and the desired extent of chemical utilization. A sensitivity analysis has shown the existence of an optimum range of injection rate below which wax removal efficiency is compromised by excessive heat loss and above which it is reduced by insufficient residence time. The major limitation of this technique is encountered for large flowlines where a possibility of re-solidification of removed wax deposits exist due to excessive heat loss. Flowlines of length less than 5 km are found to be ideal candidates as in that case, sufficiently high temperatures can be maintained throughout the journey of thermochemical spacer in the flowline which will prevent re-solidification. The simulator has been validated with field implementation results of two well flow lines where the designed jobs have been successful in removing the entire wax deposits as predicted by the simulator.