Permanently Seal Multiple Annuli

Permanently Seal Multiple Annuli Using Wel-lok™ STC ToolPermanently Seal Multiple Annuli Using Wel-lok™ STC Tool

In well abandonment operations, it is required that there are no bubbles coming from any casing string before the casings can be cut and removed for permanent abandonment. When gas bubbles are migrating through a cemented annulus, or multiple annuli, this can be difficult to remediate. Section milling and placing a cement plug in the section milled window is costly and not always effective as the gas that has migrated through the existing cement can also cut the new cement placed in the well.

Wel-lok™ offers a V0 qualified plug that is significantly shorter than cement plugs, reducing the time and cost associated with milling long windows with a proven track record of success, eliminating the potential that the well will have to be re-abandoned at a later date.

Bismuth alloys expand when they solidify, eliminating the possibility of micro-annuli forming and providing a permanent solution the first time, every time, as opposed to cements and resins which shrink. As environmentally friendly barriers, in addition to time and cost savings they also reduce carbon emissions caused by cement and rigs.

Wel-lok™ Seal Through Casing (STC)

The BiSN Seal Through Casing system is run on electric line, without the need for surface pumping equipment to circulate the alloy into place. Instead, due to its viscosity and density, once melted the liquid alloy simply flows under gravity and into the annulus, displacing well fluids.

When it cools below its melting point it solidifies but, in contrast to cement, the alloy expands on setting to create a V0 gas-tight seal across the entire wellbore. The whole process, from melting to solidification, takes place in minutes and the seal is ready to test within an hour.


  • Reduce intervention costs
  • Reduce corporate liability
  • Seal in cased or open hole
  • Deploy even in damaged and corroded tubings and casings
  • Electronically activated with no mechanical parts
  • Available in a range of sizes to suit API & non-API tubing and casings
  • Temperature ranges up to 150 °C
  • Non-corrosive and unaffected by H2S or CO2
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Dive deeper, explore the Wel-lok™ STC (Seal Through Casing)

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.

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Get in touch to find a permanent solution for your well

Businesses worldwide are benefitting from BiSN's well services in the field. Contact us today and embrace tomorrow's downhole well solution, today.

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