340-550 THEX for Reservoir Isolation During Workover for CO2 Injector

An offshore operator required high expansion bridge plugs to temporarily isolate and suspend wells during a complete workover campaign associated with converting existing gas wells into CO2 injectors. As part of the program, 4–6 wells were to be recompleted, and Interwell was requested to supply a suitable plug solution for two of these wells. The plugs were required to be run through 4 ½” 12.6# tubing with a drift ID of 3.958”, and set inside 5” 18# casing, with a restriction as small as 3.562”; caused by multiple RPT landing nipples. The plugs needed to hold up to 6000 psi (414 bar) differential pressure at temperatures up to 130°C (266°F), for roughly three months.

Interwell provided a bespoke reservoir isolation solution utilising the 340–550 High Temperature High Expansion (THEX) Retrievable Bridge Plug, selected specifically to meet the challenging downhole geometry and operational parameters of the CO2 conversion project. A full design validation upgrade from V6 to V3 was completed to align the qualification of the plug with the application requirements under ISO 14310:2008. 

The 340–550 THEX was engineered to pass restrictions as small as 3.525”; allowing it to pass the 3.562” landing nipple and expand reliably inside the 5” 18# casing.” 

The plug was designed and validated to withstand:

→ Differential pressures up to 6000 psi (414 bar) from above 
→ Temperature conditions between 100-130°C (212-266°F) 
→ Multiple tubing restrictions, including LN nipples from 3.813”, 3.750”, 3.688”, and 3.562” ID

Interwell deployed the plugs with an Electronic Setting Tool (EST) to assist in evaluating the setting prior to pressure testing. The solution provided the operator with a robust, validated high expansion mechanical barrier capable of withstanding hydrostatic overbalance pressures from the brine column above while ensuring secure isolation from the reservoir below. This approach ensured technical compliance, operational efficiency, and risk reduction throughout the workover and CO2 recompletion activities.

Both THEX plugs were successfully installed, with setting verified through a clear EST setting signature and subsequent pressure testing. To mitigate debris accumulation on top of the plugs and protect the fishing neck, junk baskets were deployed as part of the running assembly. Prior to retrieval, a targeted coiled tubing cleanout ensured that the plugs could be accessed without obstruction. 

A key challenge during the workover was the shift in wellbore conditions as the initial completion fluid was replaced with brine. This transition introduced substantial changes in pressure and temperature across the mechanical barriers. Despite this, the Interwell plugs remained fully stable and maintained verified integrity, demonstrating their robustness under variable downhole loading. 

Retrieval was performed using coiled tubing with a fishing/release tool (FRT). Engagement, release and pulling all occurred within expected operational parameters; demonstrating the effectiveness of the high-expansion design and confirming the mechanical integrity of the plug system following months of downhole exposure. 

The entire operation was executed without HSE incidents or unplanned downtime, resulting in a smooth transition to the next phase of the well conversion program. The operator benefitted from a fully verified temporary barrier solution that enabled safe workover operations in preparation for CO2 injection service. By providing a validated high pressure, high temperature expandable barrier capable of running through tight restrictions, Interwell helped de-risk the recompletion effort and reduced overall operational cost and complexity.