Study On The Characteristics Of Wax Deposition Of Wax Crude Oil Pipeline And The Countermeasure Of Cleaning And Protecting Wax

The safe and economical operation of oil pipeline is seriously influenced by wax deposition problem when waxy crude oil is transported in pipeline, effective measures must be taken. The common methods now include pigging and adding paraffin inhibitor. Although the studies of paraffin removal and control techniques in pipeline have been started for many years, but there is yet no unified standard of determining pigging period now, the related studies of action effect and mechanism of paraffin inhibitor under the interaction of multi-factor are relatively less, thus further studies are necessary.The following works were mainly finished:based on principal component analysis method, the weights of influencing factors of wax deposition were determined; taking the Zhong ning-Yin chuan pipeline as an example, the wax deposition layer thickness along pipeline under different operation conditions were predicted by using Huang-qiyu wax deposition model;3percentage of decrease in transportation amount was used as the safety limit of determining the pigging period, and the safe and economic pigging period model of the crude oil pipeline was established; aiming at lowering the daily average cost, a method of determining remnant wax thickness was given; by using the cold finger equipment, the action effects and law of paraffin inhibitor on model oil at different shear strength, temperature difference, and action time were investigated; the X-ray diffractometer and High temperature gas chromatograph were used to analyze the reasons for variation of wax deposition amount before and after adding paraffin inhibitor; by using orthogonal test, the action effects of paraffin inhibitor under the interaction of multi-factor were analyzed, the interaction between factors and important order of each influencing factor were discussed; by measuring the lattice parameters of wax crystal and carbon number distribution of deposition, the action mechanism of paraffin inhibitor under the interaction of multi-factor was studied.The research results showed that:the weight of shear stress at pipe wall, viscosity, wax molecular concentration gradient at pipe wall, temperature gradient at pipe wall decreased successively, and had a main effect on wax deposition rate; when inlet temperature was increased or lowered, the difference of maximum value of wax deposition layer thickness at same run time was within0.087mm; the lower of earth temperature, the larger of maximum value of wax deposition layer thickness; with the increase of inlet temperature, daily average cost increased, pigging period extended, while the increase of transportation amount and earth temperature lowered them; taking3percentage of decrease in transportation amount as the safety limit of determining the pigging period was reasonable and feasible, and this could ensure the safe and economical operation of pipeline; the remnant wax thickness of Zhong-yin pipeline was about0.4-0.6mm,75thousand yuan was saved yearly, but the remnant wax thickness could also not be reserved in some pigging periods; paraffin inhibition effect was better when wall temperature of cold linger was lower and temperature difference between oil and wall was larger; with the increase of shear strength, paraffin inhibition rate increased firstly and then lowered, while with the increase of action time, paraffin inhibition rate reached a constant gradually; eutectic and absorption effect of paraffin inhibitor changed the parameters of diffraction peak intensity, interplanar spacing of wax crystal, making the growth of wax crystal more regular and wax crystal become larger, thus exerted an inhibiting effect on wax deposition; after paraffin inhibitor was added, the increase of oil temperature and wall temperature lowered diffraction peak intensity, enlarge interplanar spacing of wax crystal, but with increase of action time, the effect laws were contrary to that when oil temperature increased; when shear strength increased, interplanar spacing decreased; when wall temperature remained invariant and oil temperature lowered, the percentage of wax with regular carbon number increased while wax with high carbon number decreased, the laws were adverse when wall temperature decreased and shear strength increased; the influencing important order of each influencing factor on paraffin inhibition rate was shear strength, temperature difference, and action time successively, the influence of temperature difference and shear was distinct; interaction between shear strength, temperature difference and action time was not distinct; the synchronous variation of shear strength, temperature difference, and action time did not change wax crystal shape, but change laws of lattice parameters were different to that under the effect of single factor; the distribution range of carbon number, width, change law of content of n-alkanes and isoparaffin in wax deposition were basically the same to that under the effect of single factor.