Effect Of Reheating On The Flowability Of Waxy Crude Treated With Pour Point Depressant

Waxy crude oil treated with pour point depressant(PPD)can effectively improve the low-temperature flowability of waxy crude oil below wax appearance temperature(WAT).The low temperature flowability of waxy crude oil modified with additives is very sensitive to the thermal history it experienced.Reheating temperature within a certain range can significantly deteriorate the flowability of PPD-treated crude oil and threaten the safe operation of pipelines.In the current ASTM pour point test specification,there is also a repeated heating process,which affects the testing of pour point of PPD-treated crude oil.In addition,the low-temperature flowability of PPD-treated crude oil is also deteriorated by the initial temperature of reheating.Therefore,it is of great significance for the safe and economic operation of waxy crude oil in pipeline transportation to clarify the influence of temperature on the effect of PPD during reheating.For three types PPD-treated crude oil with remarkable modification,the changes of pour point,apparent viscosity and yield stress of modified oils at different reheating temperatures and initial reheating temperatures were studied.At the same time,the wax crystal micro-imaging experiments were carried out.The results show that:(1)The modification effect of PPD becomes worse when the sample is repeatedly heated to 45 C,and the pour point,apparent viscosity and yield stress all increase.With the increase of reheating temperature,the pour point,apparent viscosity and yield stress increased first and then decreased.When the reheating temperature is lower than the wax appearance point(WAT)or higher than the wax dissolution point(WDT),the effect of reheating is not significant.When the reheating temperature is between wax precipitation point(WAT)and wax dissolution point(WDT),the flowability of PPD-treated crude oil will deteriorate,and the modification effect will even be completely lost.(2)At the worst reheating temperature,the pour point,apparent viscosity and yield stress of the three kinds of modified experimental crude oil increased gradually with the decrease of initial reheating temperature,and the low temperature fluidity of the oil sample deteriorated.The lower the starting temperature of reheating is,the worse the fluidity of additive oil will deteriorate.When the starting temperature is higher than a certain temperature(near the freezing point of blank oil),the fluidity parameters of additive oil will change smoothly.At this time,the starting temperature of reheating has little effect on the low-temperature fluidity of additive oil.