The Sealing Behavior of Bismuth-Based Metal Plugs

Abstract Bismuth-based alloy plugs are currently potential alternative to cement plugs. These metal alloy plugs demonstrated several distinctive properties, such as expanding after cooling, corrosion resistance, and being non-porous. In a previous study, several small-scale experiments were conducted on bismuth-tin (BiSn) plugs and were compared against cement plugs. Both bismuth and cement samples were subjected to extensive physical, hydraulic, and mechanical push-out tests after curing. Leakage tests using nitrogen gas were also carried out on both plug samples. Preliminary results demonstrated that bismuth-tin plugs possess much higher resistance to pressure and gas migration in the micro-annulus between the plug and the casing, thus providing better sealability in comparison to cement plugs. In this study, more light is shed on the behavior of bismuthtin metal alloy as a sealing plug where its hydraulic bond strength is further investigated with restricted axial expansion. The test setup replicates real-life well conditions where the effect of elevated temperatures and pressures is addressed. Preliminary findings indicate that with a restricted axial expansion, the bismuth plug shows elevated hydraulic bond strength since it was forced to expand radially and thus provide a perfect seal. The aim behind the conducted laboratory experiments is to understand the sealing ability of bismuth to a steel pipe and how it will change at different representative wellbore pressures and temperatures. This paper is a part of an extensive research study that at advanced stages will be addressing the sealing performance of a bismuth plug in the annulus and its interaction with the surrounding formation.