Flow Characteristics of Power-law Fluid Flow in Coiled Tubing

Author:Wang Hong Tao

Supervisor:zuo tie


Degree Year:2018





Due to the small tubing diameter,there is excessive friction in coiled tubing.More attention is paid to the downhole of coiled tubing in the field,but there is little research on the the spiral section of coiled tubing.In addition,through literature research,it is found that the research on the flow characteristics of the spiral section is difficult and not fine enough.Predicting friction pressure in coiled tubing has been an engineering challenge.Based on theory and experimental methods,this paper deeply analyzes and studies the flow of coiled tubing,and the characteristics of power law fluid in the coiled tubing are revealed.It provides a theoretical basis for the corollary equipment and the construction parameters of coiled tubing.Following the approach of boundary layer approximation analysis,solutions of laminar flow of a power law fluid in coiled tubing were obtained for flow behavior index.Based on the theoretical analysis and numerical solution,considering the influence of centrifugal force on the friction coefficient,the friction coefficient correlation of the inner laminar flow of the coiled tubing was established.Similar approach was applied to turbulent flow of power law fluid in coiled tubing.First,the flow model in coiled tubing was simplified and the tubing cross section was divided into inviscid core and a thin boundary layer.Then,the flow equations for the core and the boundary layer were simplified through order of magnitude approximations.The simplified momentum equations for the boundary layer were then integrated over the boundary layer thickness to obtain equations of momentum integrals.After assuming proper forms of velocity profiles for flow in the boundary layer,the equations of momentum integrals were converted to ordinary differential equations which could besolved numerically to get the solutions of velocity field.Similar to the case of power law laminar Fanning friction factor,the turbulent Fanning friction factor correlation was then obtained that considers the effect of centrifugal force on friction coefficient.The new correlation was also evaluated with some HUBS data.There is a good agreement between the new correlation and the HUBS results.This new correlation was verified by comparing with the Ito correlation and Mashelkar&Devarajan correlation for the special case of Newtonian fluid.There is excellent agreement between the new correlation of this study and the Ito correlation.An extensive experimental study was performed with polymer-based fluids using the lab-scale flow loops which consist of an array of coiled tubing diameter and of various tubing lengths and curvature ratios.Polymer fluids tested in this study included:xanthan,HPAM,Guar,CMC and HPG fluids at various polymer concentrations.It was found that coiled tubing curvature increased the friction pressure significantly.The maximum difference in friction factor between coiled tubing and straight tubing can be as high as 200%,depending on the tubing size,polymer concentration,and generalized Reynolds number.For Newtonian fluid,the difference in friction factor between coiled tubing and straight tubing is not as significant as for polymeric fluids.But,the friction factor difference still can be as high as 30%.Data analysis of friction pressure showed that drag reduction in coiled tubing is lower than in straight tubing.As curvature ratio increases,the drag reduction of polymer fluids in coiled tubing decreases.The most important feature is that as the curvature ratio increases,the friction factor increases.The effect of curvature ratio is also dependent on the polymer concentration.It can be seen that the correlations could adequately match the experimental data.Majority of the predictions are within 10%.The accuracy of this new correlation has been evaluated.