Casing Protection Performance Research on Hollow Microbead Cement under Evaporite Bed Creep Condition

Evaporite beds are widely distributed in oil and gas-bearing basins. Their creep characteristics exert continuous compressive forces on casing, leading to casing deformation and even failure which severely affects the lifespan and production safety of oil and gas wells. To effectively mitigate the damage to casing caused by evaporite bed creep, based on a hollow microbead cement slurry system, a buffering design scheme of “trading space for time” was proposed for casing protection in evaporite beds by utilizing the stress-relieving effect of microbead fragmentation to reduce the casing/cement sheath interfacial stress and absorb the evaporite bed creep displacement. Through laboratory evaluation tests of string deformation under a creep condition, the influence of cement with different hollow microbead contents and particle sizes on casing deformation was investigated. The results indicate that during the initial stage of evaporite bed creep, the hollow microbeads in the cement absorb formation creep displacement through fragmentation, preventing casing deformation; when the creep displacement exceeds a critical value, the casing begins to deform, and the deformation increases with the increase of creep displacement. Increasing the content and particle size of hollow microbeads in the cement can significantly enhance its ability to absorb critical evaporite bed creep displacement, effectively buffer the compression on the casing during the initial stage of formation creep, and ensure the runability of downhole tools in the wellbore before casing deformation. The research results provide a new theoretical basis and technical approach for wellbore integrity design in evaporite beds.