Mechanical Plugging Strength and Failure Risk of Low-Melting-Point Alloy in Casing Sealing

To investigate the effects of overlying axial pressure and ambient temperature on the mechanical plugging performance of low-melting-point alloy (LMPA) in casing sealing, simulation experiments were conducted with LMPA as the sealing material to clarify the underlying mechanisms. Based on the maximum shear strength theory of the alloy plug/casing interface, a metal plug forming device and a gas-tightness detection apparatus were designed. Laboratory tests were then carried out to evaluate the ultimate shear strength and gas sealing integrity of the alloy plug, followed by the analysis of forming axial pressure and ambient temperature on mechanical sealing behavior and the exploration of alloy plug failure modes under mechanical plugging conditions. Experimental results show that the ultimate shear strength between the alloy plug and casing decreases with increasing ambient temperature at an average rate of ~0.225 MPa/°C. Applying forming pressure can enhance the integrity of the alloy plug, promote its radial expansion, and thus improve sealing integrity. After sliding shear failure, alloy plugs with an aspect ratio of 2.32 lose gas tightness completely, while those with an aspect ratio ≥ 3.5 retain more than 50% of their original gas sealing capacity after sliding shear displacement. This study provides a theoretical basis and technical reference for the application of LMPA in downhole casing plugging operations.