The bismuth alloy technology is capable of permanently and eternally shutting-off gas migration in single or multiple casing annuli by forming a V0 rated Metal-to-Metal gas tight seal. For P&A operations the bismuth alloy barrier technology results in a significantly higher level of sustainability compared to the current conventional way of performing P&A operations in oil and gas wells. This requires to be acknowledged in the vision for the future of P&A which will be one of the most emission intense oil and gas activities.
This paper will explain results of recent P&A campaigns that support the above fact. Bismuth alloy barriers were deployed inside 12 section milled windows of less than 50 feet length in a recent campaign for an operator in the Middle East. The wells were successfully P&A- ed, building on a track record of a worldwide P&A campaign with the "Seal Through Casing" bismuth alloy technology with about 160 wells executed between 2015 and 2023.
The reason for the eternal barriers is related to the unique and unmatched physical barrier performance properties of bismuth. Bismuth, in its molten form, which is melted downhole using the energy generated by the thermite heater, has the viscosity like that of water (1 – 3 cps) and a specific gravity of around 10. Which means it is about 10 times heavier than water. This allows it to flow freely in all directions - into section milled windows or through perforations, crack, crevice, or micro annuli displacing any fluid in its path (Fig. 1). These bismuth alloys are eutectic in nature which means one of the properties that they exhibit is they change phase at a single sharp temperature without passing a two-phase equilibrium, i.e. liquid and solid state. Another unique property of elemental bismuth and bismuth-based alloys is that it expands on solidification, like water as it solidifies into ice. In case of pure bismuth and bismuth-based alloys this volumetric expansion ranges between 1% – 3% depending on the composition of the alloy. Bismuth based alloys once molten can thus flow into any volume or annuli and take its shape and once solidified it expands against the casing, cement or formation creating a V0 gas tight barrier.
These unique physical properties combined with high corrosion resistance nature make bismuth-based alloys the ideal candidate for long term "eternal" P&A material.