A Sealability Study on Bismuth-Tin Alloys for Plugging and Abandonment of Wells

The use of bismuth alloys as a barrier material for plugging and abandonment (P&A) has gained traction in the literature due to the large number of wells scheduled to be plugged and abandoned. In addition, many questions have been raised regarding the sealing efficiency of cement in the long run. Within this context, this work performs a thorough study of the sealability of plugs made with the eutectic bismuth-tin alloy. This effort is divided into three fronts: laboratory tests to verify the pressure resistance and leakage rate of these plugs, microscopy analyses to corroborate the tests’ insights through observations of the alloy microstructure, and numerical simulations to capture and model the involved phenomena aiming to reproduce real well scenarios in the future. Results show that bismuth-tin plugs exhibit better pressure resistance and lesser leakage rates than cement plugs, which indicates that this material is a suitable candidate. Better sealing properties are achieved when the plugs are set under higher curing pressures than the atmospheric pressure, an observation that is confirmed when observing the microstructures formed. Finally, a suitable material model that captures the expansion upon solidification is proposed, and the effect of thermal expansion on the plug and pipe assembly is observed.