Study On The Flow Properties Of Yield For Gelled Crude Oil In Pipeline

Most crude oil produced in domestic oilfield is with high wax content,high viscosity, high gel point and poor rheological characteristics. It becomes more complex and difficult to pipeline the crude oil with these features. Waxy crude oil near the gel point will precipitate a lot of wax crystals,and the precipitation wax crystals cross-links with each other to form space network structure. The network structure makes the crude oil lost mobility finally so that crude oil takes on yield stress,thixotropy,viscoelastic and so on. Yield characteristics are the one of important rheological properties of waxy crude oil. The research on yield characteristics of waxy crude oil is great important for normal pipeline and restart-up.Mainly based on experimental loop and coaxial cylinder rheometer,the paper studies on the rheological properties and the pipe flow yield characteristics of Chad crude oil. Firstly, according to the basic rheological parameters of Chad crude oil measured by rheometer,experimental loop programs is designed. In the determination of constant flow restart mode,the preliminary experiments has been conducted and the main factors of effect on Chad crude oil yield stress is obtained. Secondly,on the basis of experimental date analysis,the law of single fact effect on size of Chad crude oil yield stress is found,and make the orthogonal experimental design. By the orthogonal experiment, the impact effect of main factors affecting on changes of Chad crude oil yield stress can be evaluated and the best restart-up conditions for Chad oil in experimental loop is obtained. Finally, by using the Least Squares Support Vector Machine (LS-SVM), multiple nonlinear regression on the yield stress of Chad crude oil is carried out, thereby the mathematical expression between the yield stress and the major factors are obtained and the relationship between the yield stress and the major effect factors is quantified.Through two restart methods of constant pressure and constant flow,the transmission and distribution of the pressure along the pipeline for Nanyang and Chad crude oil are studied. Pressure along the pipeline transmission and distribution are analyzed and compared at different startup temperatures,flow rates and restart pressure. The pressure transmission speed along the pipeline is obtained at different startup conditions.