Numerical Modeling of Bismuth-Based Plugs for Well Plug and Abandonment

Plugging and abandonment of wells is a fundamental operation within the oil and gas industry, which has gained more focus recently due to safety and environmental concerns. Downhole plugs must withstand extreme pressure and temperature conditions and, in some cases, corrosive environments. Ensuring good sealability is of utmost importance considering the long-lasting perspective of P&A. The usage of plugs made of bismuth alloys is a recent technology that has been vouched as an improvement over traditional cement solutions, especially in terms of resistance to pressure, corrosion, and leakage. Bismuth has the unique characteristic of expanding upon solidification, a phenomenon that has been the main driver for suggesting it as a potential barrier material. Furthermore, creep and aging effects become relevant since the plug is placed in temperatures that could reach close to the melting point of its alloy. This paper comprehensively assesses the necessary modeling steps for characterizing the eutectic bismuth-tin alloy appropriately in commercial finite element analysis software considering the aforementioned phenomena, including a comparison with laboratory tests. Simulations are carried out to test this plug model under different downhole scenarios. Results show that the resistance of the plug to pressure diminishes when the downhole temperature increases, although the exhibited resistances seem to suffice field applications. These conclusions are intended to support bismuth in its qualification as an accepted barrier material.