Study of the paraffin deposit formation using the cold finger methodology for Brazilian crude oils

Transportation of paraffinic crude in a cold environment can result in wax depositions, which are solid deposits, on the pipe wall. The formation of paraffin in the bulk of the petroleum is a crystallization process in solution. Such phenomenon occurs along the pipe connected to offshore wells and even onshore. Its main implication is a paraffin blockage with serious economical consequences. This work aims to learn about paraffin deposit formation using a cold finger methodology, in two types of Brazilian crude oils (32 API and 20 API). The polythermal method is used in various experiments using different temperatures in both cold finger and bulk of the fluid. The experiments measure: the thickness of the deposits, as well as the deposition rates, degree of subcooling and, finally, the induction for the onset of wax. The methodology allows the evaluation of the critical time of deposition and the critical temperature difference between the hot petroleum source and the cold seawater temperature. It is shown that the deposit rate depends on this temperature difference, as well as the cooling surface, the nucleation kinetics and the growth of the crystals on the cold finger surface. The work discusses carefully the experiments design under the light of dimensional analysis. The values of critical temperature differences are relatively small and show that the encrustation is easily attained in the offshore petroleum flow. The methodology implemented is simple and allows the prediction of very important information about the mechanism of paraffin encrustation that could pave the way to avoid paraffin deposition in offshore petroleum production due to high temperature differences between the heat petroleum sink source and the cold seawater. (C) 2004 Elsevier B.V. All rights reserved.