Metal-to-metal downhole seal stands up to challenging reservoirs

Conventional elastomer-based sealing elements are increasingly challenged by unconventional reservoirs. This was the motivation for Caledyne in its development of the MTM downhole seal, a metal-to-metal sealing technology suitable for the challenging environments common in heavy oil, highly acidic, and high-pressure/high-temperature (HP/HT) reservoirs.

According to Roland van Dort, Caledyne's Managing Director, as operators have been forced to extract hydrocarbons from increasingly aggressive reservoirs, they have hit an upper limit with traditional sealing elements. "In heavy oil production scenarios, for example, you want to seal off a portion of the tubing string in order to inject steam into part of the reservoir to improve oil production. At typical steamflood injection temperatures of up to 300°C (nearly 600°F), elastomer seals will begin to break down.

"There is a similar challenge when producing from HP/HT reservoirs, or those with high levels of H₂S and CO₂," van Dort continued. "Rubber-based seals will not survive for long under these conditions."

The MTM downhole seal's innovation comes from the materials of construction employed. Rather than using elastomers as the external sealing element, a flexible metal seal is used to contact the tubing string and form a tight and durable seal that withstands high temperatures, pressures, and corrosive fluids. "The seal can be installed indefinitely," van Dort confirmed. "In most cases, it will last as long as the pipe does."

The seals can be installed on existing packers, liner hangers, and other downhole tools, and the same setting tools and loads employed on standard seal equipment can be used with the MTM seals. The company has also designed a variation of these seals to work in subsea sealing applications, such as plugs and flange seals.

Well abandonment is another application ideally suited for the MTM seals, according to van Dort. "Well integrity issues are common for abandoned wells, where over time the wells may repressurize and start to leak through inferior cement jobs. Metal seals would be particularly beneficial in these applications, as they are extremely durable over long periods of time, much longer than elastomer-based seals."

The seals are retrievable as well, and the same one can be reset to isolate different sections of the tubing string to treat different reservoir zones. "This is another important distinction compared to elastomer seals, which must be replaced more frequently," van Dort added. "This adds time and cost to your completion or fracturing activities, and increases your inventory costs."

The seal's ease of installation and retraction comes from its composition. The external metal component of the seal houses a flexible, silicon-based filler that is stable at temperatures above 340° C (644° F), which Caledyne states is suitable for 99% of the field jobs performed.

The company performed extensive finite element analysis to determine which material properties would have the greatest impact on performance, namely ductility and hardness of the metal shell and elongation and elasticity of the filler. The result was a system that deforms in a predefined manner in order to produce a tight seal, and in the event that it needs to be retrieved, the system retracts in a predefined manner as well.

Caledyne states that the MTM seals are performance rated to 10,000 psi at 300°C, and certified to ISO 14310, the international standard for downhole equipment in the oil and gas industry. Seals are currently available in size ranging from 5 in. to 9 ⁵/₈ in., with other sizes in development.

The MTM seal has been field tested in various applications over the past two years, including installation on a liner hanger during a cementing job in a North Sea well, a retrievable packer installation for a steamflood application in Kazakhstan, and installation on various downhole tools for Canadian heavy oil steamfloods. In each case, the MTM seals held, without any loss of well integrity and without the need to use special installation equipment or to change operational protocols.

"Our continued field tests are demonstrating that the MTM seal is a cost-effective answer to retrieving resources from previously untapped and difficult to reach wells," van Dort concluded.

As heavy oil is considered one of the largest worldwide reserves of hydrocarbon, Caledyne plans to expand these tests to other heavy oil markets, including California, Venezuela, and the Middle East.

To learn more about Caledyne's MTM seal technology, visit www.caledyne.co.uk, or contact Roland van Dort by email.

Ted Moon is the Technology Editor of JPT Online. He brings information on emerging technologies, R&D successes, new field applications, updates from SPE papers about recent innovations, and more. If you have a question or suggestion for future article topics, email Ted at teched@spe.org.