Numerical Model And Simulation Study Of Cement Injection Annulus Displacement

The interface boundary of cementing displacement describes the retention position of the annulus working fluid.The displacement interface between different fluids can reflect the retention and mixing of each phase fluid in the multi-phase fluid flow in the annulus.With different wellbore conditions and fluid properties,the annulus retention result and retention law have lots of different.The current displacement mechanism research is based on the annulus two-phase flow,which is hard to reflect the displacement effect of the simultaneous flow of three-phase or even multi-phase fluids in the annulus,and does not calculate the mathematical displacement model suitable for various annulus conditions.In this paper,the study of displacement law and displacement model of three-phase fluids in the annulus is developed.The main research contents are as follows:(1)Selecting the H-B rheological model as the rheological model of the annulus fluid.Based on the NS equation and the Cahn-Hilliard equation,establish a mathematical model for the annulus displacement flow,and use numerical analysis to implicit differential the flow equations.The equation is differentiated and transformed into a form that can be worked out,solved it by numerical analysis.(2)Basing on the three-phase fluid displacement principle,the physical model of the annulus flow was developed,and the annulus retention characteristics are analyzed by the method of segmentation analysis.Through the analysis method,the law and characteristics of the annulus fluid retention with different displacement conditions can be reflected,which helps to display the fluid flow state and mixing state at different depth points in the annulus displacement process.(3)Comparing the analysis of three-phase flow with the two-phase flow in the annulus by CFD software.Analyzing the flow velocity,viscosity and density,the displacement conditions,and retention of the three-phase fluid in the annulus was expounded.Combining with the experimental simulation data,the three-phase flow mathematical model considering fluid viscosity,fluid density,and injection velocity was fitted,which is in good agreement with the displacement simulation results and can provide a reference for the prediction of the three-phase displacement effect of the annulus with vertical well conditions.(4)Basing on the three-phase fluid displacement,the displacement laws of various wellbore conditions,including annulus eccentricity,annulus expansion,and eccentric-expansion diameter,are studied.Through a large number of numerical simulation analysis,the effects of various annulus conditions,different fluid parameters and different injection speeds on the annulus displacement effect were clarified,the displacement rules in various cases are revealed,and the eccentricity,expansion,and eccentricity are fitted.Mathematical model of diameter expansion、density structure、viscosity structure、flow rate change and the model calculation results are in good agreement with the verification results.This paper constructs a new theoretical evaluation method of displacement effect,which can reveal the retention mechanism,interface distribution of the three-phase fluid in the annulus,and improve the description of replacement boundary model.Based on this,a mathematical model based on eccentricity,expansion,eccentricity-expansion,density structure,viscosity structure,and flow velocity was developed,which provides a theoretical basis for the design of the three-phase displacement parameters of the annulus and lays an essential theoretical foundation for improving displacement efficiency.