Study On Displacement Efficiency Of Cementing Under Non-uniform Geometric Boundary Conditions

In order to ensure a good sealing effect in the wellbore of oil and gas Wells,it is necessary to guarantee the displacement efficiency of cementing.Therefore,the flow rules of drilling fluid and cement slurry in the displacement process should be clearly defined and the displacement efficiency should be accurately evaluated.But most current cementing displacement theory research on the rules of the ideal conditions for borehole wall,and the complicated underground conditions in the process of drilling and completion,occurring in the process of rock fragmentation rough wall of mud cake,makes the actual wall with irregular surface morphology,the existing theory to real reduction cementing displacement process fluid flow law of displacement in the annular space,causing the error on the displacement efficiency evaluation.Considering the above problems,this paper is irregular wall condition,drilling fluid and cement slurry in the eccentric annulus of the air flow pattern are studied,and evaluated the irregular wall caused by the inhomogeneous geometry boundary conditions of cementing displacement efficiency,thus for cementing parameters design and provides a theoretical guidance for the cementing quality.The main research contents and results are as follows:(1)The flow model of hercher-Barclay drilling fluid and cement slurry axial laminar flow in eccentric annulus under cylindrical coordinate system is established,and the mathematical relationship between the velocity distribution and pressure flow of Hercher-Barclay fluid in eccentric annulus is obtained.An analytical model for the conditions of drilling fluid retention in eccentric annulus is established.A numerical solution computer program is developed to calculate and analyze the location boundary,width,retention area and displacement efficiency of overall and local retention of drilling fluid.The results show that the pressure gradient in the flow field increases,the thickness of the local retention layer decreases,and the displacement efficiency increases.The eccentricity increases and the displacement efficiency decreases.Under the condition of laminar displacement flow,it can reduce the drilling fluid yield stress and increase the displacement fluid yield stress,which is helpful to improve the local retention of drilling fluid and improve the displacement efficiency.(2)To establish the uniform caliper cementing displacement flow analysis model and numerical simulation method,the evolution process of cement slurry and drilling fluid interface adopts the numerical simulation,analyzes the drilling fluid and cement slurry fluid properties,flow field of the pressure gradient,eccentricity,and poor is the density law of the influence of different conditions on the displacement efficiency.The results show that the optimal ratio of fluid displacement parameters exists in the eccentric annulus cement displacement flow,which provides theoretical guidance for construction.(3)Consider the heterogeneity of borehole wall,studied the friction loss along the fluid flow,the paper analyzes the relationship between the frictional losses and shear stress,analyses the annular drilling fluid of inhomogeneous geometry boundary wall of strength,establish the non-uniform geometric boundary wall side and casing side displacement interface boundary position calculating model,realizes the quantitative evaluation of drilling fluid retention.The results show that the deviation Angle is between 0.3 and 0.4 and the displacement fluid level is relatively stable with high displacement efficiency.The displacement efficiency is higher when the density difference between 45°and 60°is300kg/m~3 and 700kg/m~3.Under different driving pressure gradients,it is helpful to improve the displacement efficiency by increasing the pressure gradient of flow field as much as possible.(4)Aiming at the nonlinear annular geometric conditions of the non-uniform wellbore,the basic model of the lattice Boltzmann method and the surface boundary conditions are selected by using the lattice Boltzmann method,and the geometric model describing the non-uniform geometric boundary wellbore is established.The numerical simulation model of non-uniform geometric boundary condition of cement injection displacement was established.The influence law of different parameters of non-uniform shaft wall on displacement efficiency and other conventional cement injection flow parameters on displacement efficiency were analyzed.The results show that the greater the roughness,the lower the displacement efficiency;The more drastic the roughness changes,the lower the displacement efficiency,indicating that maintaining the uniformity of borehole wall can improve the displacement efficiency.In this paper,by means of theoretical derivation and numerical simulation model with the combination of research methods,the eccentric annulus cementing displacement flow in uniform and non-uniform geometric boundary wellbore two case studies,research reveals that the eccentric annulus cementing displacement flow displacement efficiency rule,enrich the cementing displacement theory,for the eccentric annulus cementing displacement parameters optimization design provides a theoretical basis for cementing operation has certain guiding significance on site.