Measurement and Prediction of the Kinetics of Paraffin Deposition

Abstract

SPE Members Abstract Economically and technically viable methods for controlling paraffin buildup in pipelines and wellbores are critical to the production of crude oil in deep water and cold environments. Laboratory test methods and a computational model have been developed to predict rates of paraffin deposition in pipelines and the effect of long-term deposition on the pipeline pressure drop and temperature profile. The model has been incorporated into a fully menu-driven program that runs on a personal computer. The two major portions of the program are the thermodynamic model which is used to calculate solid-liquid-vapor phase equilibria and the kinetic model which is used to predict the deposition and paraffin buildup rates. The thermodynamic portion is described in a companion paper. The kinetic model is based on information present in the literature and on several hundred measurements of paraffin deposition rates in a laboratory scale test loop. Introduction In subsea pipelines, flowlines, and wells the cost of controlling and remediating unanticipated problems from paraffin deposition is substantial. For this reason, Conoco has developed experimental and modeling techniques to reasonably predict the paraffin deposition potential of crude oils and condensates. This paper first discusses an experimental technique to measure paraffin deposition rates under flowing conditions at simulated operating conditions. The deposition data are used as input to a deposition model which is used to predict deposition rates and the long-term effects of deposition. The application of the deposition measurements to the testing of chemical inhibitors is also discussed. The model has been used in a number of studies of paraffin deposition in existing and proposed operations. The results of two case studies are presented. The case studies concern the long-term effects of paraffin deposition in a subsea pipeline and the potential for paraffin deposition in the start-up of a subsea pipeline. EXPERIMENTAL Description of Apparatus The apparatus used to measure paraffin deposition rates, shown schematically in Figure 1, is similar to apparatuses used by other investigators. The crude oil is first heated to 150-180 degrees F in a sealed system to melt any paraffin present while avoiding the loss of light ends. During a run, the remelt bath is maintained at a temperature significantly greater than the cloud point. The oil is pumped from the remelt bath through the tempering bath where it is cooled to the desired inlet temperature. P. 353^