Metal-to-Metal Seals Meet Downhole Hazard Demands
Authors: van Dort Roland 
Published: February 2015

Technology Update
As oil and gas production activities continue to shift toward more hostile and unconventional environments, such as reservoirs with high-pressure/high-temperature (HP/HT) or very acidic characteristics, the use of elastomeric sealing materials in wells and subsea piping face limits to their durability and reliability.
Seal failure can have major safety and environmental consequences, as well as resulting in costly repairs and lost production. The record of failures of critical liner-hanger seals in HP/HT completions, for example, has become a large concern. Operators globally have been adopting the most rigorous quality-assurance procedures for these seals to prevent dangerous and costly incidents. As many as 18% of offshore wells worldwide are estimated to have some form of weak-ness or uncertainty in their integrity. This includes a sizable number of abandoned wells that may repressurize and leak through damaged or poor cement jobs.
Rubber-based seals are used throughout the production industry. However, they begin to break down in HP/HT reservoirs, in downhole settings high in H2S or CO2, or in thermal-recovery applications where temperatures may approach 600°F. In addition, rubber-based seals on retrievable devices can be damaged and compromised by downhole debris, including during retrieval operations.
In response to the shifts occurring in the producing environment, and to other downhole operating risks, metal-to-metal (MTM) sealing technology capable of withstanding extreme temperatures and pressures—and debris impact as well—has been developed by Caledyne. MTM technology provides the safe, cost-effective seals needed in packers, bridge plugs, flange seals, and other components for many of the most challenging projects to proceed (Fig. 1).

Metal-To-Metal Seal Systems
These MTM systems employ a flexible metal seal, rather than an elastomer, as their external sealing element to contact the surrounding tubing or pipe and form a tight, durable seal that withstands HP/HT and corrosive-fluid conditions in the well even when they are changing and volatile. To achieve the needed flexibility, the metal sealing element houses silicon-based filler that is stable at temperatures above 644°F—with higher-temperature filler currently being tested. The MTM seals are certified to ISO 14310, the international standard for oil and gas industry downhole equipment, and performance-rated to more than 15,000 psi at 572°F. Available in a wide range of sizes, MTM seals can be installed indefinitely and in most cases will last as long as the pipe.
In addition to their technical benefits, MTM seals provide a commercial advantage because each seal is suitable for any downhole condition, regardless of temperature, pressure, corrosive reservoir environment, or the chemicals injected downhole. Thus stock levels of seal equipment can be minimized.

Case Study: Retrievable MTM Bridge Plug Deployment
A Caledyne-manufactured retrievable bridge plug (RBP), incorporating the MTM seal, was deployed successfully for Talisman recently on the Bunga Kekwa project in Malaysia to temporarily plug the BKC-20 gas well (Fig. 2).