Modelling hydro-mechanical coupling effects on creep-induced compaction deformation around boreholes

The current research on rock compaction deformation around boreholes rarely considers the coupling effect of pore pressure in the rock body and the heterogeneity of rock porosity, which cannot reflect the failure mechanism of borehole compaction under actual working conditions. In this paper, a viscoplastic constitutive model is used to numerically study the compaction deformation mode of high-porosity saturated sandstone under the influence of fluid-structure coupling effect. The fluid effect is introduced through the UMAT-UMATHT framework, and the evolution characteristics of the effective stress field under different stress states and reservoir pressures and its influence on the localization mode of the compaction zone are discussed. The results show that the change of reservoir pressure can significantly change the stress path and local deformation mode of the rock. In addition, the pore structure heterogeneity has an important influence on the localization pattern. The compaction zone tends to develop preferentially in the high porosity region, while it is significantly suppressed in the low porosity region. Although the influence of the Biot coefficient is limited under homogeneous conditions, it significantly enhances the effect of the porosity heterogeneity under heterogeneous conditions, intensifies the expansion of the local compaction zone, and makes the plasticized region more extensive.