Effects of the porous structure of cement sheaths on the deformation failure mechanism of wellbore cement sheaths

Abstract

Two types of cement sheaths with different porosities were prepared by using cement materials and liquid silicon suspension. The distribution characteristics of the pore radius and space location of two types of cement sheaths were analyzed using CT scanning experiments and statistical principles to obtain their probability density distribution functions. Based on the distribution functions, the “single-layer” and “double-layer” porous models of two types of cement sheaths were constructed using a self-developed program incorporated with the FLAC 3D program. A series of numerical simulations were conducted to study the deformation and failure laws of wellbore cement sheaths under in situ stress and hydraulic pressure. The effects of the porosity and double-layer structure on the breakdown pressure, plastic failure zone, radial deformation, and stress distribution of the cement sheaths were analyzed. As a result, the effect mechanisms of the porosity and double-layer structure on the failure mode, failure path, and interaction between the cement sheath and metal casing were revealed. The failure modes and paths of single- and double-layer cement sheaths were obtained. This research provides a basis for understanding the characteristics of stress distribution, deformation, and failure mode of porous cement sheaths under hydraulic pressure.