Successful High Expansion Water Shut Off Deployment for Major Operator in Oman

Plug and Abandonment with Wel-lok™ Seal Through Casing (STC) Tool

An onshore well in Oman was producing water from a lower perforated interval.

The customer required a tool that could pass through a narrow restriction of 3.50” in the tubing and remediate this water production out to the 8.25” open hole.

The customer was faced with retaining a rig and pulling the tubing to remediate the water producing zone.

BiSN was contracted to provide a high expansion solution that could be deployed through tubing without using a rig saving the operator substantial time and money.

BiSN provided a Maximum Drift tool (MXD) designed for water shut off applications that flows molten bismuth alloy into the tiniest fractures and voids, passing through the narrow restriction while still providing a seal to full well diameter.

The plug was successfully set in minutes, not days, with zero non-productive time.



The operator needed a solution that didn’t involve pulling the tubing.

Pressure and Temperature: Although the deployment did not fully meet High Pressure High Temperature conditions, setting depth parameters of 14,295ft and 8055psi meant using specialist high temperature alloys for the plug material to counter the amplified effects of the environment.

Narrow Restriction: Restrictions in the well necessitated the diameter of the BiSN tool string to be 97°C no larger than 3.25”. This prevented the use of cast-alloy tools due to the geometric limitations.

Due to this challenge the Wel-lok™ MXD (Maximum Drift Tool) tool was selected allowing unique BiSN alloy beads to be deployed past the restriction in sufficient volume to form an effective plug.

Using the MXD tool which utilizes bailers and heaters in the same string, allowed us to make a highly effective plug in one single run giving significant time and cost savings.

High H2S Environment: The well presented a highly corrosive environment with 6% H2S present. With the corrosion-resistant properties of BiSN alloys, and by using NACE compliant materials in the MXD tool itself, the job was completed without impact from the H2S, and the plug formed a long-term barrier without threat of corrosion.


The MXD tool string was composed of a modified thermite heater, a timer activated MXD electronics assembly, an internal pressure activated bailer release mechanism and bailers containing BiSN alloy beads.

The tool string was run to depth. The bailer release was then activated and all the alloy beads from the bailer was dumped around the thermite heater below.

Minutes later, the thermite heater was activated, setting the plug. After allowing the bismuth alloy to solidify, an overpull was taken to verify that the plug was set. The MXD tool string was then removed from the well.


Successfully set a plug, in minutes, at ~15000 feet, ~100°C and ~8000psi out to 8.25” past a 3.5” restriction using BiSN Wel-lok™ MXD tool (Maximum Drift Tool).

Business Value

While traditional sealing methods like cement squeezing would have taken the client at least 10 days to complete, BiSN’s Wel-lokTM plug sealed in minutes and was ready to test within four hours. After our successful deployment the operator is bringing the well back into production.

  • Rigless operation
  • No need to pull the tubing
  • A permanent sustainable seal was set
  • Successful Water Shut Off between 7” liner and 8.25” open hole
  • A permanent plug that’s not impacted by high H2S conditions
  • Project completed with 0% Non-Productive Time

Talk to our technical team today to find out more.

About the application

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, 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.

Seal Through Casing - BiSN
Seal Through Casing - BiSN
Seal Through Casing - BiSN
Seal Through Casing - BiSN

How it works…

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.

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.

This is a required field
This is a required field
Please enter a valid email
This is a required field
This is a required field

Don’t miss out on the latest technical updates and advancements. Subscribe today.

Please enter a valid email address.

Our website uses analytics, marketing and preference cookies to both provide the most relevant experience for our users and to give us information about how our site is used. By clicking “Accept All”, you consent to the use of these cookies. However, you may visit "Cookie Settings" to provide a controlled consent.

Accept All Cookies