Calculating Method for the Axial Force of Washover String During Extracting Casing in Directional Well

In the process of extracting casing in directional well, the existence of inner casing and external centralizer makes the calculation of washover-string axial force more complex, which increases the difficulties for choosing a reasonable bit weight in construction with no doubt. In this paper, through taking three factors of casing contacting with washover tubing, centralizer and washover tubing contacting with well wall into consideration, an effective method for calculating the axial force conducting is established. Moreover, the axial force in different conditions is obtained through numerical solution. The calculation results are: (a) The casing has a less effect on the axial force conducting, and the axial force loss is mainly at centralizers and new contact points. (b) The axial force conducting can be improved effectively through setting a reasonable centralizer spacing. There is no doubt that the establishment of the method has an important significance for choosing the bit weight, judging whether the washover head cuts casing and designing washover string. Key words: Axial force; Washover string; Extracting casing; Frictional resistanc