Well-Abandonment Solutions Use Bismuth and Thermite Effectively and Safely

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193118, “Well-Abandonment Solutions Using Bismuth and Thermite,” by Paul Carragher, SPE, and Jeff Fulks, BiSN Oil Tools, prepared for the 2018 SPE Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 12–15 November. The paper has not been peer reviewed. Traditional methods of abandoning a well by use of cement and bridge plugs are still common practice among most operators globally. Although resins have been used as an alternative, no major developments have been made in well-abandonment materials for nearly a century. This paper demonstrates a new way to create gas-tight seals during well abandonment, overcoming the limitations of traditional methods and reducing the operator’s liability and potential environmental impact after decommissioning has been completed. Statement of Theory and Qualification Testing Bismuth has multiple commercial uses outside of the oil and gas industry. The idea of using bismuth for sealing in downhole environments is not new; the earliest patents were filed in the 1930s. Bismuth possesses many unique qualities, including Relatively low melting point (273°C) compared with other metals Viscosity very similar to water when in liquid form High density, with a specific gravity of 10 Noncorrosive and unaffected by hydrogen sulfide or carbon dioxide Expands approximately 3% upon solidification Nontoxic (used in place of lead in some commercial applications for this reason) Eutectic metal, converting from liquid to solid state almost instantaneously when it cools below its melting point, bypassing the gel phase The challenge in creating a seal with bismuth has always been how to deploy it downhole—melting it and then causing it to solidify and expand where the seal is required. Previous attempts were made with electrical heaters. These heaters required large amounts of power (480 V and 11 A to generate 540 kJ of energy) for hours to melt a relatively small amount of bismuth alloy. Voltage drops in the electric line limited the depth at which the tool could be run in the well. After melting, the electrical heaters could not keep the bismuth in the liquid phase long enough for it to reach the sealing area and fill the void it was intended to seal. To obtain the energy necessary for this application, thermite was considered as a heating element. Thermite is a combination of iron oxide and aluminum powder. When these are combined in the correct chemical composition and activated, a reaction occurs that results in byproducts of aluminum oxide, iron, and large amounts of heat. To activate the chemical reaction, thermite must be heated to a temperature greater than 2000°C; the resulting output is in excess of 10 000 kJ. The temperature at which the thermite burns can reach as high as 2000°C. For the thermite heating element to be used with the bismuth, the burning temperature would have to be controlled and consistent. To accomplish this goal, binding and damping agents were added to the thermite. The binding agents ensure that the chemical composition of iron oxide and aluminum powder remains consistent without separating, resulting in a repeatable reaction. The damping agents control the amount of heat generated and the speed at which the reaction takes place.