Low-throughput Operation Characteristics Analysis And Safe Assurance Technology Research Of Waxy Crude Oil Pipeline

A typical waxy crude oil in Daqing oil field pipeline is transported in the way of heating transportation. Due to the declining production of oil field, the pipeline throughput is dropping year by year, thus the crude oil pipeline is vulnerable to a unstable state, which easily leads to the congelation accident. In the waxy crude oil pipeline process, the dissolved wax molecules in oil will continuously crystallize and deposit on the pipe wall, making the effective circulation area decrease and the flow resistance increase. Therefore, in order to ensure the safety operation of pipeline, the low-throughput pipeline operation characteristics are studied. The unstable factors affecting the low-throughput operation is summarized. And on the basis of that, the sensitivity of the factors which influent the safety throughput is analyzed. Combining the calculation results, the safe and economic transportation way of the low-throughput operation is determined.The research mainly includes the following contents:First, from the point of low-throughput operation characteristics, the effect of low-throughput operation on the pipeline safety and economy is analyzed, in order to determine the pipeline safety throughput. The factors of low-throughput operation are also pointed from the perspective of hydraulic characteristics and thermal characteristics, respectively. And through the principal component analysis, the impact of pipeline throughput on wax deposition is determined.Second, the allowable minimum throughput under thermodynamic condition and the allowable minimum throughput of pipeline characteristics are calculated by using the black oil network model of PIPESIM software. Then according to the actual situation of pipeline under low-throughput condition, several kinds of common assurance technologies are summarized, including modified delivery, namely the addition of pour point depressant and modification of heat treatment, and positive and negative transportation technique, etc.Third, the single factor sensitivity analysis and multi-factor sensitivity analysis based on orthogonal test of safety throughput factors are done by PIPESIM simulation software, respectively. The sensitivity degree of these two methods under different factors is determined, and the different causes are proposed by comparing the analysis results of them.At last, based on the conclusion of sensitivity analysis, the feasibility of conventional method to ensure the waxy crude oil pipeline safety low-throughput operation is analyzed. And an economic and feasible preliminary reference project is proposed, by making economic and technical comparison to different schemes.