New pressure-activated sealants help operators stop pesky leakage in subsea wellbore and control systems.

Despite dramatic advances in subsea engineering capabilities, the pressures and temperatures in increased water depths create an environment that's highly conducive to leakage. During the life of a subsea system, leaks can occur in most of its components. And it's not just casing or valves that leak - the bottom line leaks, as well. Having an alternative to mechanical workover when repairing subsea leaks not only clears the operator's mind, it also clears the way for greater production and profitability.
As engineers evaluate solutions to any subsea problem, their first step is to analyze the problem then review alternative solutions. Restoring pressure integrity is no exception. Typically, mechanical well workover - including component replacement - is the obvious option. But it's also an expensive one, since considerations for subsea intervention include rig availability, service company availability and management, replacement equipment and lost production. There's also the cost of mobilizing an appropriate intervention vessel. And there's always the risk of failing to reestablish production after the procedure. By any measure, repairing leaks of all varieties via mechanical workover is an expensive endeavor.
Leaks and the cost of pressure
Not only are leaks expensive, but they're one of the most painfully prolific problems in the oil patch - particularly in the subsea environment. While no leak is typical, engineers are expected to deal with each one appropriately and economically. Some are well within normal engineered operating limits, requiring only monitoring. Some call for action and analysis, but not on an emergency basis. Others need to be addressed immediately for safety reasons or for compliance with operating guidelines. This may even call for well shut-in.
Since there are several components in these complex systems, there is a variety of leak types. Connection leaks are found in umbilical lines, hydraulic lines, control systems, flow hubs, tubing, casing and similar components. Dynamic seal leaks occur in the seals of moving parts, such as surface-controlled subsurface safety valves (SCSSVs), actuators, valve control systems and other components. Static seal leaks occur in nonmoving seals and often are seen in wellheads, packers, hangers and other downhole hardware.
Damage to components during installation can result in a variety of leak sources. Downhole, these leak sources include tubing, casing, packers, sleeves and other components. Anywhere you have pressure, a troublesome leak waits in the wings.
First-generation sealants
But there is some good news. During the past decade, the use of sealants as a short-term solution for maintaining productivity has given operators new options for returning wells to safe operation. Specially engineered sealants are an alternative to mechanical workover, at a fraction of the cost. Onsite leak repair - in which a repair team injects sealant into the leaking system - requires only a single person, a small amount of equipment and none of the usual workover hassles.
But conventional sealants have a one-track mind. They will seal everything, not just the leak. Sealants traditionally used in subsea environments are activated by temperature, time or simply by clogging the leak with particulates. Valves and other critical wellbore components also can be gummed up, demanding careful analysis of the cost, benefits and scenarios involved in the procedure. Conventional sealants also can damage hydraulic or wellbore components permanently. However, sealant technology has grown more intelligent during the past decade.
'Smart' sealants
The latest generation of sealants gives subsea operators the best of both worlds: the economies of avoiding a workover without sacrificing capital equipment or safety. These "smart" sealants are pressure-activated and specifically designed to seal leaks in wells and other severe-environment hydraulic systems quickly and effectively.
Pressure-activated sealants remain fluid in any hydraulic system or well until they reach the leak site. There, at the point of differential pressure, the sealant's polymerization reaction bridges the leak, creating a strong, flexible seal. The reaction is analogous to blood coagulation in the human body. Instead of simply clogging the leak with particulates - which can increase the risk of plugging other vital components - the seal is established through a chemical process.
Subsea sealants are used on SCSSV systems, subsea control systems and other applications where there are tight flow tolerances in the equipment. The developers of this technology performed 25 sealant operations on subsea equipment in 2001 with a 92% success rate.
Technically speaking
Contrasted with particulate sealants, pressure-activated subsea sealants are composed of monomers and polymers in a carrier fluid. These fluids have been proven to pass through a 5-micron filter and still seal a significant leak. That enables effective sealing of the leak site without clogging hydraulic filter systems or affecting fluid cleanliness. They're designed to be compatible with hydraulic fluids and mechanical components in the well. The properties of the carrier fluid vary, depending on the project. However, since pressure-activated sealant polymerizes only at the point of differential pressure, the remaining sealant fluid can remain in the system or be flushed out.
A case-specific evaluation of the procedure and sealant composition results in this isolated sealing mechanism. Engineers experienced with this technology are able to inject a custom-blended sealant formula using procedures adapted for the particular conditions of the leaking system - whether it be tubing, casing, a wellhead or an SCSSV.
Process and procedure
Initial indications of a leak may be dramatic, or they may be negligible. Pressure may show up in unusual places or make itself known in higher- or lower-than-expected readings. Fluid levels may rise or drop. Control systems may kick in automatically to keep pressure at normal operating levels. Monitoring systems may detect the leak. Control functions may fail, or safety systems may shut the well in.
Realization that a leak exists should kick off the analysis phase of the leak-sealing project. The repair team should analyze the data to determine if the solution is pressure-activated sealants. Based on this analysis, the repair team should develop a procedure to address the well in question and pass it on to the operator for approval. Crews then should implement the sealant process.
Delivery methods for pressure-activated sealants depend on the leak's nature and parameters. For subsea applications, the selective sealing quality of these sealants allows for several delivery methods. A technician can pump the sealant through existing umbilical lines to the leak site or through a temporary umbilical - even by a remotely operated vehicle to a hot stab. The sealant will not harden in the umbilical or during delivery, regardless of time, temperature or ambient pressures.
Subsea component testing
Independent laboratories, as well as Cameron, Amerada Hess, Norsk Hydro and Petrobras, performed compatibility and performance testing of pressure-activated sealants with subsea components. They conducted the tests on varying component types to validate the technology and ensure the protection of equipment subjected to the sealants.
Subsea control valve testing. Crews simulated a leak in a Cameron subsea control valve by crimping the metal-to-metal seal. They verified the leak's severity by pumping nitrogen through the damaged valve while it was suspended in water, then injected the pressure-activated sealant. The polymerization process quickly established a seal. After the seal cured for a brief period, workers raised the pressure to the operational limit of 5,000 psi. To further determine seal strength, they increased the pressure on the valve to 7,000 psi. As a final test, they cycled the valve to verify that its full operational capabilities were maintained. The engineers were able to cycle the valve with no loss of hydraulic fluid. They cured the leak, and the valve returned to operation.
Umbilical testing. Petrobras conducted rigorous capability testing of pressure-activated sealants in umbilical lines and SCSSV mechanisms. Crews created simulated leaks in umbilical system fittings, connections and hoses while damaging or removing seals in SCSSVs to create severe leaks. The pressure-activated sealant was able to stop all leaks except where cuts in the control lines were deep. The flexible seals held at the rated equipment pressure of 5,000 psi.
Compatibility testing. Petrobras assigned CDA & Associates to conduct compatibility tests of pressure-activated sealants. The tests proved the sealants did not damage the materials found in the well. Testing also proved the sealants had superior attributes when compared with glycol- and petroleum-based hydraulic fluids.
The ability to return a valuable, high-production subsea well to production within days of a leak-induced shut-in - without a conventional intervention - is significant. At a time when technology improvements and their accompanying marketing hype are often at risk of becoming a distraction, rather than enabling operators to exceed production goals, it's refreshing to find low-profile technical innovations that have high impact. And if today's operators need anything from advancements in technology, it's the providence of more and better alternatives.

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