Sealing Performance of Sn58Bi Low-Melting-Point Alloy for B-Annulus Plugging Under Cyclic Loading

In geological carbon storage, cyclic casing loading can induce micro-annuli in the B-annulus cement sheath, risking CO₂ leakage. Compared with conventional cement, the Sn58Bi low-melting-point alloy boasts excellent flowability and favorable elastoplastic behavior, emerging as a promising sealing alternative. This study focuses on enhancing wellbore integrity by using Sn58Bi alloy to seal the B-annulus cement sheath. An experimental system was established to simulate micro-annulus evolution, with gas migration tests conducted under cyclic internal pressure to systematically evaluate the effects of temperature and cyclic loading on the alloy’s sealing performance. Additionally, a three-layer casing–annulus–formation coupling model was constructed to investigate the radial displacement of the Sn58Bi alloy sheath and cement sheath at 30 °C and 20 MPa casing pressure, clarifying their distinct mechanical responses. Results show that the alloy’s sealing performance improves with temperature (30–90 °C), while elevated cyclic internal pressure accelerates gas breakthrough and reduces sustainable cycles. Under identical conditions (30 °C, 20 MPa), Sn58Bi alloy exhibits significantly superior CO₂ sealing capacity to conventional cement. This study confirms the alloy’s potential for enhancing wellbore integrity and provides theoretical support for its application in B-annulus plugging during subsurface carbon storage.