Effect of buoyance on casing central degree of high angle deviated well

In order to install centralizers in high angle deviated wells rationally and decrease the risk of casing running, it is significant to figure out accurately the effect of buoyance generated by the difference of density inside and outside the casing on the casing central degree.In this paper, the model for analyzing the forces on centralizers was modified and a chart describing the influence of density difference between inside and outside the casing on the casing central degree was established.And the change of density difference between inside and outside the casing over the time in the process of displacement was also taken into consideration.Thus, the centralizer installation method for high angle deviated wells in Chenghai Oilfield was developed.Calculation results show that the maximum increment of casing central degree due to buoyance is 36.4%, 19.6% and 12.2% when the centralizer installation spacing in the area of Chenghai is 30 m, 20 m and 15 m.The higher the hole deviation angle is and the higher the density difference between inside and outside the casing is, the larger the variation of central degree is.When the centralizer installation spacing is 10 m, buoyance gets weak and maximum variation of central degree is only 6.2%.It is in nonlinear positive correlation of cubic polynomial between centralizer installation spacing, sine of hole deviation angle, density difference between inside and outside the casing and central degree variationunder the effect of buoyance.It is shown from the practice in Well ZH29-30 that the casing central degree design method which takes the buoyance into account can improve the displacement efficiency of cementing and ensure the safe running of casing.