Abstract
ABSTRACT: In certain shale formations, time-dependent creep deformation can naturally close the annulus between the borehole and casing, potentially forming a self-sealing barrier without conventional cement. While previous studies have demonstrated this concept under idealized axisymmetric conditions, field applications inevitably involve casing eccentricity and in-situ stress anisotropy. This study develops a 2D plane strain finite difference model incorporating a Burgers–Bingham viscoelastic–viscoplastic constitutive formulation, calibrated against laboratory data on Pierre II shale, to predict shale barrier formation under these non-ideal conditions. A parametric study evaluates the effects of dimensionless casing eccentricity and stress anisotropy ratio on borehole convergence, casing contact patterns, and stress buildup. Results show that eccentricity produces asymmetric closure with delayed full contact on the wide-gap side, while stress anisotropy concentrates creep-driven deformation along the minimum horizontal stress direction, leaving azimuths aligned with the maximum stress partially open. A sealing efficiency metric, derived from stressdependent annulus permeability, is applied to quantify barrier quality over time. The framework provides a practical tool for assessing shale barrier feasibility under realistic field conditions.