Used in Other Industries and Repurposed for Oil and Gas: Bismuth ?Alloy as a Proven Solution for Downhole Leaks Intervention

Abstract In the periodic table, there are many elements unfamiliar to mainstream engineers. Some of these elements are metals, such as bismuth, which possess unique properties that can be utilized for various purposes. Bismuth is a metal that is safe to handle, melt, and even ingest for medical purposes. The use of bismuth is common in cosmetics, glass, ceramics, solders, and sprinkler systems. Over the past decade, this metal has been repurposed for use in the energy industry, particularly to address leaks occurring downhole. When mixed with other metals such as tin and silver, bismuth forms a low-temperature alloy with valuable sealing properties. Sustained casing pressure (SCP) is a common well integrity issue caused by pressure communication from the reservoir reaching the surface. This occurs due to cement channeling or casing-cement micro-annuli. Bismuth allows for the creation of a molten metal downhole with the viscosity of water and 10 times its density. Upon solidification, similar to ice, the metal expands to create a gas-tight metal-to-metal seal. To avoid SCP, particularly from gas leaks, many measures are taken, such as enhanced cement formulations, gas-tight casing connections, and other chemical solutions. However, when SCP is still observed, an intervention method is required. After pinpointing the exact source of the leakage, a section mill is performed in the area of the suspected leak. If cement is present behind the opened section, a scraper is used to remove it. Traditionally, several methods have been employed to seal the area, such as resin, cement squeeze, and casing patches. However, these methods require optimization. The method described in this paper involves using a metal that can be molten downhole to provide a metal-to-metal seal in the area of concern. Given its unique properties and expansion characteristics, a gas-tight seal can be achieved. This concept has been extensively tested in the yard using full-scale casings and simulated downhole pressure and temperature conditions.