Study On Wax Deposition Law Of PD Crude Oil Pipeline

Wax deposits on the pipeline wall reduce the pipeline transportation capacity.If the deposits are not removed timely,it may result in serious blockage of the pipeline.Therefore,wax deposition simulation is of great significance in ensuring safe waxy crude pipeline operation.The PD pipeline transports high-viscosity,high-gel point,and high-waxy crude oil.As the oilfield production decreases,the PD pipeline output gradually decreases,resulting in faster temperature drop and an increase in wax deposition rate.This paper compares the representative wax deposition models at home and abroad,selects the most suitable model to simulate and analyze the wax deposition profile along the pipeline under the low flow rate conditions and determines the corresponding pigging cycles.The China University of Petroleum(Beijing)model,the Matzain model,and the Michigan aging model are analyzed and compared from the aspects of modeling mechanism,experimentally determined parameters,wax precipitation characteristics,and temperature gradient calculation methods.The above three models are used respectively to simulate the wax deposition regularities of Number 1 crude pipeline and Number 2 crude pipeline.Compared with the other two models,it has the following advantages to use the China University of Petroleum(Beijing)model to simulate wax deposition profiles.First,the use of this model eliminates the need for loop experiments,which facilitates engineering applications.Second,this model uses the DSC experimental test method to obtain crude oil wax precipitation characteristic parameters.The test process is simple and the test results are more accurate than that of thermodynamic calculation method.Third,the simulation results of the model are quite reliable.China University of Petroleum(Beijing)Wax Prediction Model and the corresponding software are used to simulate the wax deposition profile of PD crude oil pipeline.The effects of factors such as season,the transportation flow rate and deposition time on wax deposition rate and wax distributions are studied.Reasonable pipeline pigging cycles under different operating conditions are put forward.As the output gradually decreases,the location where wax initially precipitates will advance and the wax deposition rate will increase.The wax deposition rate is greater in winter than in summer.The maximum wax deposition rate along the pipeline ranges from 0.19 mm per day to 0.31 mm per day when the output is 60 KBPD to 90 KBPD,and the pigging cycle ranges from 14 days to 27 days.The pig with discharge holes is selected for pigging,and the pig bypass ratio is 4% to 5%.