An operator in Kazakhstan needed a deep-set Plug and Abandonment seal as part of their rock-to-rock barrier. The operator required a solution that could isolate the entire wellbore, creating a multi-annular barrier in a zone with well-bonded cement behind the outer casing. To ensure the barrier would fully prevent gas migration, a V0 impermeable seal was required. BiSN’s STC technology was chosen, representing the first deployment of a bismuth plug in Kazakhstan, and ensuring that a durable and dependable plug was the foundation of the P&A barrier.
Deep Set Deployment: The barrier was to be set at nearly 10,000 ft which presented operational challenges during the deployment of the STC. The deployment required using bismuth beads that are deployed from surface through drill pipe. To form a good plug, operational procedures were designed to ensure the beads reached the setting depth at the right time.
Well Preparation: To form a seal out to the surface of the 9-5/8” casing, a window was section milled and cleaned. Removing all of the cement that had been in the annulus between the 7” and 9-5/8” was crucial to ensure no leak paths compromised the bismuth seal.
The BiSN STC tool is the premier P&A tool to ensure a gas-tight seal in multi-annular wells. The operator needed to set an impermeable barrier that they could be confident would isolate any gas migration and form a permanent plug. They also needed the expertise and experience to ensure that the job would be executed smoothly, given the setting depth of nearly 10,000 ft.
The well was prepared by section milling a 21m window in the 7” and flushing the zone to remove debris. An inflatable bridge plug was set at the bottom of the window to form a base upon which the bismuth beads that would be melted to form the plug would be deployed.
A thermite heater was connected to drill pipe with a timer-activated running tool. Based on the expected duration of the operation and expertise gained from hundreds of tool deployments, an activation time was programmed, and the tool string was deployed to the setting zone.
Once at depth, beads were deployed into the drill pipe and allowed to fall via gravity to the setting zone. The drill pipe was flushed to ensure that they had reached setting depth and that the drill pipe was clear. When the timer expired, the thermite heater was activated and began melting the bismuth alloy. After a short melting period, the thermite heater was removed from the plug, leaving a solid barrier across the entire wellbore. The alloy then cooled and solidified, expanding to form a gas tight plug.
The deployment resulted in a verified 1.4-meter bismuth plug. The ability to set a short plug that was gas-tight as the foundation of the barrier allowed for a reduced section mill window, resulting in significant time and cost savings for the operator. The durable plug ensures that the well will stay sealed, protecting the environment and the operator continually.
Seal Reliability and Durability
Permanent Wellbore Isolation
Operational Efficiency
Cost Reduction
The wel-lok™ STC (Seal Through Casing) has been developed to achieve a gas tight V0 seal well annuli that cannot be achieved by traditional cement balance plugs. Run on electric line, coil tubing or drill pipe, this tool does not need surface pumping equipment to circulate the alloy in place. Due to its viscosity and density, once melted the liquid alloy will flow with gravity into the annulus. When it cools below its melting point it solidifies, expands and creates a gas tight seal across the entire wellbore. The entire process, from melting to solidification, takes place in minutes and the seal is ready to test within an hour.
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