Study On Improving Cementing Quality By Shear Turbulent Flow In Annulus On The Basis Of The Casing Executing An Eccentric Revolution

The shear swirling flow vibration cementing technique rotates the downhole eccentric cascade by circulating cementing fluid during.It makes the casing eccentrically revolve at high speed around the axis of wellbore.It produces strong agitation action to the annulus fluid and makes it in the state of shear turbulence.A great deal of work has been done on the study of eccentric annulus flow.The studied flow types include Poiseuille flow,Couette flow,spiral flow in the eccentric annulus and the annulus flow with the inner cylinder executing a planetary motion.The study on the shear turbulent flow in annulus with the inner cylinder executing an eccentric revolution has not yet been carried out.The mechanism of the shear turbulent flow in annulus increasing cementing quality in the case is not clear.Moreover,the shear turbulent flow field with the casing executing an eccentric revolution of has an adverse effect on the stability of the borehole wall and casing string vibration.It is harmful to the safety of vibration cementing.In view of the above problems,the paper studied on the improving cementing quality by shear turbulent flow in annulus on the basis of the casing executing an eccentric revolution.The mathematical model of the shear turbulent flow in annulus on the basis of the casing executing an eccentric revolution in the moving bipolar coordinates was established based on the transform relation between inertial Cartesian coordinates and moving Cartesian coordinates and the transform relation between bipolar coordinates and Cartesian coordinates,using time-averaged principle and the k-? turbulence model.And a wall shear stress calculation model concerning wall roughness was derived.The finite volume method was used to solve the mathematical model.The distribution of characteristic parameters of the shear turbulent flow in annulus was obtained.A mathematical model for characterizing fluid instability and the formation conditions were proposed.On the basis,the mechanism of improving the cementing quality with the casing executing an eccentric revolution was analyzed.On the one hand,the activation mechanism of mud cake was put forward based on sediment incipient motion theory.Considering the influence of compactness,fluid viscosity and pressure difference,the critical shear stress model of mud cake activation was established.The influence of wall shear stress on the mud cake with the casing executing an eccentric revolution was calculated and analyzed.On the other hand,the effect of vibration on the gel strength of drilling fluid and cement slurry was studied by laboratory tests.The effect of the improved performance fluid on improving cementing quality was analyzed.By establishing the calculation model of casing eccentricity,the action distance of the downhole eccentric cascade was obtained,that is,the range of the improved performance fluid.In addition,the wellbore stress calculation model considering the influence of vibration pressure was established.Improving the calculation method of turbulent friction coupling and considering Poisson coupling,the casing coupling vibration model with the vibration pressure as driving force was established.In order to ensure the safety of well cementing,the cementing operation parameters,the structural parameters of the downhole eccentric cascade and the casing string structure were optimized.In the paper,the study of eccentric annulus flow was enriched by establishing the mathematical model of the shear turbulent flow in annulus on the basis of the casing executing an eccentric revolution in the moving bipolar coordinates.The mechanism of improving cementing quality was perfected.And the cementing operation parameters,the structural parameters of the downhole eccentric cascade and the casing string structure were optimized,which provided a theoretical basis for the optimal design of vibration cementing.