Plugging and abandonment (P&A) is a part of the decommissioning process for wells in the oil and gas industry. Once the wells are no longer used for production or deemed uneconomical, the wellbores are plugged and sealed to stop further leakage. P&A prevents greenhouse gases like methane and other harmful crude oil products from leaking into the environment, safeguarding both the ecosystem and offshore marine life.
Traditionally, cement has been the primary material used for plugging and sealing wellbores. However, cement is not completely impermeable and will deteriorate over time due to factors such as temperature fluctuations, chemical reactions, and mechanical stresses. Unfortunately, several instances of cement plugs leaking and releasing harmful substances into the environment have been reported. To ensure the long-term integrity and stability of these abandoned wells (the plug should last up to 3,000 years to qualify for deployment in North Sea, as stated by OGUK), bismuth alloys have recently emerged as groundbreaking plugging material.
Why Use Bismuth Alloys?
Expansion upon solidification: Bismuth alloys can be engineered to expand slightly, by 3-6%, upon solidification, unlike the shrinkage and consequently circumferential fractures observed with typical cement. This ensures a tight mechanical bond with the wellbore casing and within the annuli outside the casing, enhancing the effectiveness of the seal.
Melting point: The melting point of bismuth-based alloys for different compositions can range from 124 °C to 330 °C. This characteristic allows more efficient and controlled deployment of the alloy without affecting the wellbore-casing, and also temporary plugging and maintenance. The choice of a specific alloy with an appropriate melting point can be based on the wellbore temperature, casing material, and the heating technology employed.
Composition variability: Bismuth alloys offer flexibility in terms of composition. By adjusting the percentage of individual metals, such as tin, silver, antimony, and indium, different variations of bismuth alloys can be created. This allows the customization of physical, mechanical, and chemical properties of the alloys to suit varying wellbore characteristics.
Permeability: The bismuth alloys have zero bulk permeability ensuring complete sealing across the bulk.
Long-term durability: Bismuth alloys exhibit resistance to corrosion, brine, CO2, and crude oil, and maintain structural integrity at high temperatures. These properties ensure the longevity and effectiveness of the plugging material.
High density and low viscosity: The combination of high density and low viscosity allows the melted alloy to penetrate narrow and hard-to-reach areas of the wellbore without the need for a pump. Voids, irregularities, and fractures within the wellbore are filled more effectively with melted alloy than with cement. 
Non-toxicity: Bismuth alloys are non-toxic and environmentally friendly unlike cement, which contains additives and chemicals that can contribute to soil and groundwater contamination.
Economical: The cost of well-decommissioning ranges from $100,000 per well onshore to $1-10M per well offshore. Cementing and rig costs alone account for more than 25% of the total decommissioning cost for offshore wells. The higher cost of alloy to cement is overshadowed by the elimination of cementing and rig cost.
In addition, low thermal expansivity, improved thermal fatigue, high mechanical strength, pressure rating and creep resistance of bismuth-based alloys have presented them as potential and the most sought-after material for plugging and abandonment of gas wells in the recent years. Leaders in the oil and gas companies funding its development show how vital it is for the future of the P&A process.
Indium Corporation has carried out a huge amount of in-house research on fusible alloys. We have the ability and expertise to fine-tune the characteristic of bismuth-based alloys as per customer and industry needs. If you are interested in, or working with the application of bismuth-based alloys in P&A and any other industry, please share with us your needs, and problems if you are facing any. Let’s plug the wells together.