Model Of Drilling Fluid Retention And Two-phase Flow Interface In Well Cementing

The quality of cementing directly affects the life of oil and gas wells and oil and gas production.Improving cementing displacement efficiency has always been the primary goal of cementing construction.In order to analyze more objectively and accurately the flow rule of cement displacement in solid wells,analyze the factors that appear to be trapped in drilling fluids,establish a circular residual model of drilling fluids,and explore the characteristics of fluid flow and retention interface changes.This paper is based on the differential equations of fluid motion under column coordinates.The axial flow equation of the eccentric ring of Heqieer and Baerkelai was established.The flow velocity function,apparent viscosity function,and semi-analytical numerical solution of flow-pressure drop flow parameters were established.The analysis conditions and calculation models of integral and localized residual hydrodynamics of eccentric ring drilling fluids were established,and the phase lag boundary and core width of eccentric ring drilling fluids were calculated by model simulation.The effects of relevant factors on drilling fluid retention were calculated and analyzed.Combining the pure mechanics theory model with the mixing and diffusion between fluids,a two-phase liquid interface change simulation experimental device was independently designed.Experimental tests and analysis were conducted on the interfacial changes of drilling fluid and displacement fluid,and an empirical model was established for the analysis and calculation of parameters such as thickness and density of interfacial mixing layer.It provides the basis to explore the ways and measures to improve the technology of cementing and replacing.The model simulation shows that with the increase of casing bias,the retention of drilling fluid becomes more serious.When the casing eccentricity is low,the drilling fluid retention is mainly concentrated in the narrow gap,and the maximum retention layer is located on the wall of the well.With the increase of the casing bias,the retention area of the drilling fluid gradually spreads,and the retention area increases,with the increase of the shaft slope angle.The thickness of the residual layer at the pipe is gradually increased and more obvious,and there is a slight change at the wall of the well,but the change is not obvious.The thickness of the retention layer under different pressure gradients is also different.The higher the pressure gradient,the smaller the calculated retention layer thickness.When the pressure gradient is close to 1500 Pa/m,the retention layer thickness is approximately 0.Through the two-phase flow interface change test,it is obtained that the change of rotation speed and mixing time have a significant influence on the rheological performance of the fluid in the mixing layer.The rheology index and shear force will increase with the increase of speed and time.The density and consistency coefficient will decrease with the increase of speed and time.A theoretical basis for evaluation of drilling fluid retention is obtained by fitting various variables.