Case study: Analysis of the correlation between casing deformation and fracture zone in Changning Block, Sichuan

Casing deformation is an engineering problem that restricts the efficient development of shale gas in the Sichuan Basin. This paper analyzed the correlation between 67 casing deformation points and 256 fracture zones in the N201 wellfield, and conducted a statistical analysis of the distribution of the orientation of fracture zones, which may have/have not caused casing deformation. The Mohr–Coulomb criterion was used to analyze the stress state and the slip risk of these fracture zones. The results show indicate the following. (1) Fracture zone is the main factor leading to casing deformation. (2) Fracture zones with 60°–90° and 110°–120° orientations are likely to cause casing deformation, whereas fracture zones with 50°–70° orientation are relatively less likely to cause casing deformation. (3) The analysis of stress state shows that the orientations of high-risk fractures range from 74°–100° and 130°–160°, the orientations of medium-risk fractures range from 64°–74°, 100°–130°, and 160°–170 °, and the orientations of low-risk fractures are in the range of 0°–64° and 170°–180°. The theoretical results are basically consistent with the field statistical results. These results provide an explanation for the field statistical results in theory. This work not only demonstrates that a fracture zone is the major geological factor that causes casing deformation, but also provides a feasible method for us to predict the casing deformation in the future.