Study On Wax Deposition Mechanism Of Oil-Water Two-Phase Flow In Shearing Fields

As a relatively general technology pattern in the petroleum industry,the process of oil-water mixed transportation is the same as that of waxy crude oil.During pipeline transportation,when the oil-water two-phase flow is transported in an environment that is below its WAT,the heavy paraffin and some cycloalkane,as the major compositions of wax,will continuously precipitate,crystallize,and adhere to the wall of temperature difference,then the crystallization core is provided and wax deposition is formed along the pipeline,which increases the pressure drop of pipeline,reduces the pipeline transportation capacity,and improves the operation costs.With understanding the threat and influence factors of wax deposition,it is of great significance to enrich the wax deposition theory of waxy crude oil by revealing the deposition behavior of oil-water under complicated working conditions.Therefore,under the background of the actual oil field gathering and transportation project,this paper considered shearing action on the microscopic level,and the morphology and aggregation behavior of wax crystals were described and characterized,the flow characteristics of pipeline flow were related to the work of shear flow field at the macro level.The oil-water two-phase pipeline wax deposition model was established from the perspective of energy analysis.Thus,the law and mechanism of wax deposition were described in the oil-water two-phase shear flow field.With the shear action increasing,the characteristic parameters including roundness,roundness variance,particle size and variance of wax crystals were all significantly reduced,the morphology of the wax crystal was changed into the regular shape,and the aggregation behavior was inhibited.At the same shear action and temperature,with the increase of water content,the characteristic parameters of wax crystal changed from increasing to decreasing near the reverse phase point.At the same shear action and water content,the wax crystal morphology and structure tended to the regularization as increasing the temperature.Based on the quantity balance relationship of wax deposition for the oil-water two-phase pipeline,the mechanism was distinguished and its quantitative description relation was constructed by introducing the shear energy,the model of oil-water two-phase pipeline wax deposition was established on the analysis of the shear energy,and then the co-deposition behavior was considered.The establishment of the oil-water two-phase wax deposition model had realizedthe prediction of the rule under the influence of gathering temperature,moisture content and flow rate.When the transport temperature was higher than the temperature which was below the freezing point of crude oil about 5 ℃ under the conditions of ground temperature in different seasons,the wax deposition rate increased with the temperature decreasing,and when the transport temperature was lower than the temperature which was below the freezing point of crude oil about 5 ℃,the wax deposition rate decreased with the temperature decreasing.With the increase of the water content in oil-water two-phase flow,the wax deposition rate decreased.However,the decreasing tendency of wax deposition rate was significantly slow near the phase inversion point of oil-water two-phase emulsification system.The rate of wax deposition decreased as the flow rate increasing.The wax deposition model,which was based on the shear energy analysis,had a good applicability to describing the co-deposition behavior of oil-water two-phase flow in the shearing field.The average relative deviation between the prediction value of wax deposition rate and the relevant literature test values was 3.20% ~ 6.79% under different working conditions.