储备库轻质原油静置沉降规律研究

Research on the Static Settlement Laws of Light Crude Oil in Reserve Depots

大型原油储罐内原油沉降分层问题是目前储罐管理运行亟待解决的重大风险之一,原油沉降分层会造成储罐有效容积减少、罐内油品损耗增加及其他不可预估的经济损失,同时,为储罐的运行管理带来安全隐患。选取某储备库有代表性的轻质原油储罐,开展了储罐原油现场静置沉降试验,在试验过程中采集储罐上部和底部油样,测定了油品的黏温关系、析蜡特性、密度以及沥青质含量,监测并分析了储罐内原油的沉降规律。结果表明:在轻质原油饱和烃含量高、沥青质含量低的溶剂体系中,原油中沥青质的溶剂化效应较弱。由于储罐内原油长期储存过程的老化效应,原油中沥青质的溶剂化层容易变薄并剥离,导致沥青质在原油中失稳、聚集并沉降,在密度差的作用下,以失稳沥青质为主的沉积物在储罐底部堆积并形成了具有较大黏度、密度的沉积层。试验得出储罐原油在静止储存60天后基本达到沉降稳定的沉降规律,为储罐搅拌周期的合理制定提供了理论依据。

The sedimentation and stratification of crude oil in large crude oil storage tanks is one of the major risks that urgently need to be solved in the management and operation of storage tanks,which will cause a decrease in the effective volume of the storage tank,an increase in the oil loss inside the tank,and other unpredictable economic losses.Meanwhile,the sedimentation and stratification of crude oil also bring safety risks for the daily operation of storage tanks.In this study,a representative light crude oil storage tank from a certain reserve depot is selected to conduct on-site static sedimentation experiments on the crude oil in the tank.During the experiment,oil samples are collected from the top and bottom of the storage tank,and the viscosity-temperature relationship,wax precipitation characteristics,density,and asphaltene content of the oil are measured.The settling law of the crude oil in the storage tank is monitored and analyzed.The results show that the solvation effect of asphaltene in crude oil is weak in the solvent system of light crude oil that possesses a high saturated hydrocarbon content and low asphaltene content.Due to the aging effect of the crude oil in the storage tank during the long-term storage process,the solvated layer of asphaltenes in the crude oil is easily thinned and peeled off,which in turn causes the asphaltenes to destabilize,aggregate,and settle in the crude oil.Under the influence of density difference,sediment mainly composed of unstable asphaltene accumulates at the bottom of the storage tank,forming a sedimentation layer with high viscosity and density.The experiment shows that the crude oil in the storage tank basically reaches settlement stability after 60 days of static storage,which provides a theoretical basis for the reasonable formulation of the stirring cycle of storage tanks.