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A method for casing-centralizing design in extended-reach wells with optimized cement displacement efficiency
BU Yuhuan1, ZHANG Daqian1,2, GUO Quanqing1
(1.School of Petroleum Engineering in China University of Petroleum, Qingdao 266580, China;2.CNOOC Energy Technology & Services-Human Resources Company, Tianjin 300452, China)
Abstract:
In an actual wellbore, two forms of casing eccentricities can develop due to the gravity effect. One is the overall eccentricity where the casing approaches downward toward the wellbore wall, and the other is partial eccentricity that is engendered due to the bending of casing between the adjacent centralizers. Both forms of the eccentricities can adversely affect the degree of the casing centralization, and this effect is much pronounced in an extended-reach well. The limitations of the current casing centralization standard were analyzed on the basis of the calculation method in SY/T 5334-1996 (the industry 's standard). An improved method was proposed for the casing 's centralization design in extended-reach wells, which can increase both of the degree of casing centralization and the displacement efficiency of cement. The model was built under the condition of the ultimate eccentricity, and then the influential parameters were analyzed. The results show that the centralized positioning of casing can be assured in extended-reach wells by properly improving the dynamic shear force of cement slurry while reducing that of drilling fluid, and increasing the density difference of the two fluids. However, the method of adjusting density difference between cement slurry and drilling fluid is not applicable for the wells with the deviation angle of 90 degrees (i.e. in horizontal wells).
Key words:  extended-reach wells  casing center degree  displacement efficiency  casing eccentric  ultimate eccentricity