Finite-Element Studies of Near-Wellbore Region During Cementing Operations: Part I

A wellbore cement sheath is expected to provide zonal isolation and borehole integrity during well construction and well life. Mechanical interactions of the cement sheath to existing and operationally induced stresses. along with other elements ill proximity to the wellbore, have increasingly large technical, economic, and environmental ramifications. Staged-finite-element procedures during well construction consider sequentially the stress states and displacements ill and near the wellbore. The model replicates complicated stress states arising front simultaneous action of far-field stresses, overburden pressure. cement hardening and shrinkage, debonding at the interface, and plastic flow of cement sheath and rock formation. At present, temperature, flow, and poroelasticity effects are not included. The technique tracks the time-dependent behavior of cement Slurry, curing (with or without shrinkage), and hardened cement during the critical period after slurry placement. Material models for casing, cement, and rock formation and failure criteria for cement, formation, and interface bonds were calibrated using published information and experimental data. Calculations were conducted for various loading and unloading scenarios, geometric configurations. properties of rock formations, and cement-slurry formulations. Results are discussed ill terms of field implication:, for example: (1) Interface microchannels may or may not develop, depending upon shrinkage magnitudes and (2) simplifying modeling assumptions that are often used, Such its 2D stresses and/or deformations, may obscure critical casing, cement. and formation behavior ill the wellbore region and in the producing horizon. This paper, part of if series quantifying the interacting physical and processes at and near the wellbore region, initiates components, useful comparisons of analytical results and field realities. The series illustrates and compares results and practical implications from simple to increasingly complex, but more realistic, assumptions, such as isotropic/directional-stress states and isotropic/anisotropic casing. cement, and formation-material parameters.