剪切作用对加剂原油凝点影响的数学模型

剪切作用是影响加剂原油流动性的主要因素之一.现场测试数据及实验室数据表明,剪切作用引起的加剂原油凝点上升幅度与剪切前加剂原油的降凝幅度(加剂原油的凝点与空白原油凝点的差值)之间有很好的相关性.基于对加剂原油剪切效应实验规律的分析,建立了对不同原油具有一定通用性并能较好地描述剪切后加剂原油凝点与剪切过程粘性流动熵产关系的数学模型.借助该模型,只须知道空白原油的凝点以及剪切前加剂原油的凝点,即可确定经过一定熵产的剪切后,加剂原油的凝点.对于加剂大庆原油、加剂新疆混合原油以及加剂中原原油的294组数据,模型计算结果与实验测结果偏差小于1℃的占50%,偏差小于2℃的占86.8%,平均偏差仅为1.12℃.该模型的建立为实现对管输过程中加剂原油流动性变化的数值模拟打下了基础.

A mathematical model for shear effect of gel point of crude beneficiated with pour-point depressants

Shear is one of the major factors influencing flow properties of waxy crude beneficiated with the pour-point depressants(PPD). The data obtained from pipelines in operation and laboratory experiments reveal that there exists a good relationship between the gel-point increment due to shear and the gel-point reduction of the non-sheared beneficiated crude,which is defined as the gel-point difference between the virgin crude and the crude beneficiated with PPD before shear.On the basis of the general rules of shear effect,a mathematical model for correlating the gel-point of the sheared-PPD-beneficiated crude oil and the entropy generation due to viscous flow in the shear process and being applicable to other crude oils was developed.By using this model,the gel point of the PPD-beneficiated crude oil sheared at any entropy generation can be predicted,provided that the gel points of the virgin crude and the PPD-beneficiated crude before shear are known. Among a total of 294 data of gel points obtained from the PPD-beneficiated Daqing crude,PPD-beneficiated Xinjiang blended crude and PPD-beneficiated Zhongyuan crude,compared with predicted values,one half has a deviation within 1℃,and 86.8 percent of the data has a deviation within 2℃.The average absolute deviation of gel points predicted by the presented model is 1.12℃.This model provides a basis for numerical simulation of flow behaviors of PPD-beneficiated crude in pipeline transportation.