Mathematical modeling and prediction of the retention layer during cementing

In the process of cementing during drilling oil well,owing to effect of the viscosity resistance,slurry cement closer to borehole wall and casing can't be displaced by drilling mud during the process of cement paste displacement,and then retention layer comes into being. however,there is no analytic equation to calculate the thickness of retention layer. according to the boundary condition of mud flowing,the exact analytical equation that calculates the thickness of retention layer of bingham fluid under different circumferential angle in eccentric annulus was derived. in addition,the changes of retention layer thickness under different central degree and different flow rate circumstance were calculated. the results of analytical computation show that the thickness of retention layer increases gradually from the wide gap to the narrow gap,and the thickness has little change in the wide gap with the increase of central degree,while in the narrow gap it significantly reduces. moreover,the thickness of retention layer reduces significantly with the increase of flow rate,but the difference of the thickness of retention layer between the first and the second cemented interface varies little. © 2014 pakistan journal of statistics.