Wax deposition law and OLGA-Based prediction method for multiphase flow in submarine pipelines

Abstract

In this study, the effects of wax deposition on submarine multiphase pipelines are investigated. In order to understand the mechanism of wax deposition in submarine multiphase pipelines, a wax deposition model in a submarine pipeline was established using the OLGA wax deposition module, and key factors influencing this phenomenon were analyzed. Additionally, a multifactor impact analysis of wax deposition was performed via the orthogonal test method. The results indicated the relative influence of five factors on oil-gas-water three-phase wax deposition, namely, oil flow rate, water content, inlet temperature, gas-oil ratio, and outlet pressure. Then, the main influencing factors of wax deposition in a multiphase pipeline flow were extracted, and the wax deposition prediction model was established. The wax deposition rate under different operating conditions was simulated using the OLGA wax deposition simulation module. The SPSS software was used to perform nonlinear regression analysis under different working conditions. In this manner, the constant terms in the wax deposition prediction model for a submarine multiphase pipeline were obtained. The prediction model could be used to programmatically predict wax deposition along a multiphase pipeline by programming the initial waxing conditions. By using this method, the wax deposition prediction model of an M − N submarine multiphase pipeline was obtained under different working conditions. After comparing the predicted and the OLGA simulation results, it was concluded that the established wax deposition model can be used to accurately calculate the wax deposition in a submarine multiphase pipeline within an allowable error range. If the physical properties and operating parameters of the conveying medium in a multiphase pipeline are given, the developed oil-gas-water three-phase wax deposition model can be used to predict the distribution of wax deposition in submarine multiphase pipelines without laboratory experiments. The results of this study can help production units understand the waxing situation of pipelines in time in order to scientifically formulate a pigging plan and avoid pipeline blockages and shutdowns.