Subsea Tubing Leak Repair

Read an excerpt from the Technical Paper

A subsea gas production well flowing to a Tension Leg Platform in 3500 feet water depth in the Gulf of Mexico failed to pass the MMS integrity test executed on the production annulus in February of 2003. A Departure package was submitted to MMS and approval received to continue producing the well pending corrective action by July 2004.

Operator contacted Seal-Tite® and a plan was developed to prepare, test and execute the leak repair operation. Custom blended sealants were prepared and a mock-up test with operator’s actual subsea equipment was performed in Seal-Tite’s shop. The corrective action plan was presented by operator and Seal-Tite® to the MMS, and the sealant repair operation was performed from the Tension Leg Platform in January, 2004. Sealant was pumped down a methanol injection line in the 7900 feet long subsea umbilical and routed into the production annulus of the well. The sealant (designed to fall through methanol and float on the packer fluid in the well) settled across the leak site in the tubing string. With flowing tubing pressure at 742 psi, annulus pressures of 2500 psi, 3000 psi, 3500 psi and 4000 psi were applied to cure the leak. The annulus was tested and held stable at 4000 psi for 24 hours. The excess sealant in the methanol injection line was flushed into the flow line and the well returned to normal operations.

The tubing leak was repaired and MMS integrity test passed without having to stop production from the well. No need for operator to resort to plan B (replacement of the tubing string), which provided a operator estimated cost savings of 7 to 12 million U.S. Dollars.

Subsea Wellhead Leak Repair

A subsea well in 1500’ water depth was experiencing a hydraulic leak to the sea in the 1/2” NPT fitting for the SCSSV at the entrance to the tubing spool on the tree. A dummy pod was connected to the tree by ROV.  Seal-Tite® sealant was pumped from the ROV’s belly tank via hot stab into the dummy pod to the leak site. The leak was sealed successfully to 10,000 psi.

Subsea Control Valve Testing

A simulated leak was created in a Cameron sub-sea control valve by crimping the metal-to-metal seal. The severity of the leak was verified by pumping nitrogen through the damaged valve while the valve was suspended in a vat of water. Once the leak had been verified, the Seal-Tite® pressure activated sealant was injected. A seal was established quickly during the polymerization process, and allowed to cure for a brief time before raising the valve to the full operational pressure of 5000 psi. To show the strength of the seal, the pressure on the valve was increased to 7000 psi. As a final test, the valve was cycled to verify that the full operation capabilities of the valve were maintained. The engineers were able to cycle the valve with no loss of hydraulic fluid; thus, proving that the leak was cured and the valve was fully operational.

Subsea SCSSV Leak

A subsea well, capable of producing 7,000 BOPD and 15MMcf/day, shut-in due to a leak in a 15,000 psi SCSSV. A Seal-Tite® technician was called to the platform and within four hours of performing diagnostics, the SCSSV leak was sealed and the hydraulic system was holding 15,000 psi. Revenue in excess of $250K was brought back on line.

Subsea SCSSV and Stab Seal Leaks

A North Sea operator was experiencing multiple leaks at a depth of 155 meters from (1) the SCSSV control line to the void cavity via the tree/tubing hanger stab seals, and (2) from the cavity to the annulus via the 2″ stab seals. The control line feeding the well was a “spur” off of a central manifold, so it was not prudent to inject sealant into the entire SCSSV system. In addition, there was no hot-stab placement on the junction plate to facilitate placement of the sealant. Divers constructed a manifold assembly and work umbilical. To successfully seal both leaks, a Seal-Tite® engineer injected one sealant blend down the control line and a different blend into the cavity.

Sealant placement operations were performed by manipulating the manifold valves. The operation was completed successfully and the leaks were cured.

Subsea Completion Leaks

Gas was observed bubbling from a sub-sea location in 1,200 ft. of water. Video captured from an ROV showed gas bubbles coming from the sub-sea completion assembly. Diagnostics performed by a Seal-Tite® technician indicated a tubing hanger leak. Using a temporary umbilical to deliver Seal-Tite’s pressure-activated sealant to the hanger void area, the sealant was injected through the leaking hanger seals. As the sealant polymerized within the leak site, the bubbling subsided and then, stopped. The leak was sealed and pressure tested to 3000 psi.

Subsea Wellhead Leaks

A large gas flow was escaping from a sub-sea wellhead in South America. A temporary umbilical was connected to the void area of the suspected source of the gas. Seal-Tite® was pumped and the leak cured to 3000 psi.

Subsea Actuator Valve Leaks

The seals in the actuators for both the wing and master valve on a Brazilian well were leaking large amounts of gas at a depth of 110 meters. For each actuator sealant operation, Seal-Tite® sealant was pumped down a temporary umbilical to the grease fitting of the actuator. The leaks were sealed and the actuators cycled, verifying that the dynamic seals of the actuators could hold pressure during cycling.

Subsea Actuator Valve Leaks

A well in South America was experiencing multiple gas leaks to the sea from the tree cap and two actuators at a depth of 275 meters. Seal-Tite® technicians sealed all leaks using a temporary work umbilical deployed from a dive support vessel (DSV).

Subsea Crossover Valve Leak

Norsk Hydro was experiencing a leak in a crossover valve on a subsea well in 300 meters of water. The leak was causing communication from the production flow line back into the annulus vent line system. Using an ROV, a temporary umbilical was deployed to the subsea wellhead and hot stabbed into the annulus vent valve. The cross-over valve was opened, and the Seal-Tite® sealant was displaced past the cross-over valve and into the production flow line. After closing the cross-over valve, the sealant was pushed through the leak site by pressurizing up on the production flow line. The seal was rapidly established, and later tested to 6500 psi.

VX Cavity Leaks

A North Sea operator was experiencing multiple leaks from the production tubing to production annulus through the VX cavity stab seals and from the VX cavity to the sea through the tree gasket release. The equipment was located at a depth of 400 meters. The leak was repaired by installing a temporary work umbilical (500 meters) into the hot stab for the VXT port. Seal-Tite® sealant was injected into the cavity and multiple leak sites were sealed simultaneously.

Subsea Flowline Hub Leaks

A flow line hub for a Brazilian well was experiencing a leak of 2.3 liters per minute. Seal-Tite® sealant was delivered by umbilical to the flow line hub. The leak was cured and pressure cycled between 0 psi and 3000 psi.

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