Study On Wax Deposition And Cleaning Cycle Of Submarine Waxy Crude Oil Pipeline

When transporting waxy crude oil in submarine pipeline, wax deposition is a big hidden danger for safe running of pipeline. Researching on the rules of wax deposition in submarine pipeline and working out reasonable and economic pigging periods can not only ensure the safe operation of pipeline, but also cut operating cost, which has an important benefit both in socially and economically. The research is based on and also the essential part of a scientific collaborative project with an offshore oilfield.This paper has taken loop experiment and computer simulation as the research methods for studying the law of wax deposition and pigging periods of subsea waxy crude pipeline. First, tested oil samples’ physical parameters and rheological properties. Next, according to the field condition, selected appropriate oil sample and main experimental parameters for wax deposition experiment. Then, set the simulation parameter values consistent with those experimental conditions, and conducted deposition simulation by using DepoWax in PVTsim software, as well as a comparative analysis on results of the simulation and experiment. Afterwards, simulated the paraffin precipitation process in the subsea pipelines. Finally, taking power consumption and pigging cost as the objective function, established the pigging period model and calculated optimal periods by Visual Basic programming, simultaneously, described the effects of oil temperature and output on pigging periods and operating cost.The analysis on oil samples’ rheological characteristics has shown that abnormal points, wax precipitation temperatures declined after blending light oil, and flow characteristics at low temperature turned better. In loop experiment, a few wax deposit began to appear on the pipe wall after about4hours, and then increased with the running time. The speed of growth overall appeared fast firstly and then slow, and the higher the fluid temperature, the more obvious this trend became. Through the comparative analysis of simulation and experimental results, it can be inferred that the wax porosity under experimental condition is around80%and it has been verified the validity of DepoWax simulation for that the simulation results had a similar regularity with experimental results. The wax deposition simulation of submarine pipeline of East China sea has indicated that, the higher the inlet fluid temperature or the bigger the mixture ratio, the more later the initial location and peak segment of wax precipitation along the pipeline emerged, and, the larger the output or porosity, the thicker the wax deposit got. Taken BYT to Pinghu DPP line as an example, the calculation of optimal pigging period under different transportation conditions has described that the optimal period increased with rising temperature and decreased with growing throughput, while the operating cost had an opposite tendency.