Mechanical analysis of casing-cement ring under non-uniform in-situ stress during inclined well drilling

Key words:  inclined well  coordinates transformation  casing-cement ring  stress distribution  deviation angle

Abstract:

In order to perform the mechanical analysis of the casing, cement ring and nearby formation in an inclined well drilling, the three principal formation stresses were transformed into a new coordinate system constituted of the borehole axis and the plane perpendicular to the axis. Under the new coordinate system, three new stress tensors were obtained, which can be used as the basis for the boundary condition to establish the relevant control equations. The stress distributions on the interfaces between casing, cement and formation in the inclined well system were calculated using the new three principal formation stress relationships, along with the variations of the stress distribution with different deviation angles. Analysis results show that the variations of the stress distribution with the deviation angle are different because of the differences in the three principal formation stress relationships. Under certain geological conditions, the anti-collapse capability of the casing in a horizontal well can be greater than that in a vertical well, and vice versa, if the geological condition changes.