Utilizing BiSN’s wel-lok™ Cement Repair Tool (CRT) to keep the well in operation.
See Tool SpecificationAn operator in Louisiana had a gas storage well with damaged annular cement. To keep the well in operation, they needed a solution that would restore the annular seal while leaving full-bore access to the entire well depth. The BiSN wel-lok™ Cement Repair Tool was chosen for its ability to make a gas-tight annular plug in damaged cement with the core of the plug milled out to restore the wellbore.
Annular Preparation: To ensure that the bismuth plug totally seals off the cross section of the 4-1/2” x 7-5/8” annulus, proper conditioning of the well is required. Frequently, the leak path in cemented annuli occurs at the cement-to-steel bonding interfaces. As the bismuth alloy melts, it has a viscosity similar to water, allowing it to flow via gravity through very small micro annuli. However, achieving access to leak paths that may be isolated from the wellbore can be challenging, especially along the inner surface of the outer casing.
Full Wellbore Access: The operator required access to the bottom of the well after the repair was completed. This required a solution that could be milled out without compromising the effectiveness of the seal. A technology that was proven to be millable without causing plug failure was necessary.
Wireline Deployment: To keep costs down and the operation on schedule, it was required to be able to deploy the tool on wireline. This allowed the plug to be set without waiting on a rig, creating a seal while preventing costly delays. Then, when a rig was available, the inside of the wellbore could be milled through to provide full cross section clearance.
The BiSN Cement Repair Tool is the most effective method for rigless annular cement repair. First, a zone with bad cement is selected after careful review of bond logs and other well data with BiSN technical experts. This ensures that a program can be planned to ensure a gas tight seal can be formed across the entire well profile.
During the deployment, perforating guns were deployed to the setting depth and activated to penetrate into the 4-1/2” x 7-5/8” annulus. This not only provides access to the annulus, but also breaks up the cement and creates channels through which the alloy can flow. A millable base was then set just below the perforating zone. This allows the bismuth alloy to build up inside the 4-1/2” pipe and flow out via gravity into the annulus.
The CRT, which consisted of a thermite heater with bismuth alloy cast on the outside, was then deployed to the setting depth. Once at depth, the thermite was activating, melting the alloy. The alloy flowed out through the perforations in the annulus, filling the voids and micro annuli in the cement. After a short melting period, the thermite heater was removed from the plug and brought to surface.
The deployment resulted in a plug that successfully passed a pressure test, indicating that the entire cross section had been successfully sealed. The well was then left to wait for rig availability, when the plug would be milled out to restore access to the entire well depth.
The wel-lok™ CRT (Cement Repair Tool) was developed to eliminate sustained casing pressure, or casing vent flow, in cemented annuli. Unlike traditional methods of perf and squeeze or perf and wash, this tool does not require any surface pumping pressure to squeeze or circulate the sealing material into place. The tool is also run rigless on electric line, sealing through casing perforations, so section milling is not required. The bismuth-based alloy has no porosity and solidifies to create a seal in minutes as opposed to hours with traditional cement and resins, eliminating the possibility of a micro-annulus being formed to allow future gas migration. If full bore access is required, it can be milled out and still maintain a gas tight seal in the annulus.
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