Analysis Of Cementing Displacement Flow In Annulus With Variable Diameter

Due to the complexity of cementing displacement flow process,most experts and scholars studied cementing displacement flow from the uniform and smooth wellbore wall.However,the condition of variable well diameter is more in line with engineering practice,so it is necessary to study the problems of cement displacement flow under the condition of variable well diameter.In this paper,we first introduce the underlying theory of fractal,and determine that the W-M function is a suitable model to describe rough wall profiles with fractal properties.The engineering properties of W-M fractal function and the physical significance of the parameters of W-M model(D,G and n)are analyzed,and the W-M fractal well diameter is characterized by the W-M fractal function,which can better reflect the essential characteristics of the actual non-linear well walls.Based on the fractal parameters of the study,FLUENT numerical simulation software was used to calculate the cement replacement efficiency of H-B fluid.The uniform well wall was set as the control group to analyze the substitution time,injection speed,well oblique angle,positive density difference and the influence of well wall irregularity on cementing cement substitution efficiency.The results show that in the actual construction process,when the change rate of borehole diameter is between 0% and 15%,that is,the relative roughness of nonlinear borehole wall is less than 3mm,the fractal dimension D is less than 1.55,and the scale parameter G is less than 3.76,the borehole wall irregularity can be ignored and the borehole wall can be considered as uniform.With the increase of displacement time,the cementing displacement efficiency increases gradually.With the increase of injection rate,cementing displacement efficiency increases gradually.With the increase of well inclination,displacement efficiency decreases gradually.With the increase of positive density difference of drilling fluid and cement slurry,displacement efficiency increases gradually.The more irregular the shaft wall is,the lower displacement efficiency is.The faster the roughness changes,the more obvious the displacement efficiency decreases.The results reveal the displacement efficiency and its influence law of cementing displacement flow in annulus with variable diameter.The cementing displacement theory is summarized,which provides theoretical support for the optimization design of cementing displacement parameters of variable diameter shaft wall,and has certain guiding significance for the actual construction operation in the field.