Zonal isolation tools, including bridge plugs and straddle systems, using metal-to-metal sealing technology in place of conventional elastomers may radically challenge existing engineering philosophies by providing a pressure sealing system capable of exceeding the limitations of other existing sealing technologies and eliminating many traditional failure modes. Metal-to-metal sealing technology is an innovative type of high expansion seal that uses expanding metal to form a high integrity pressure seal and incorporates an extraordinary seal performance envelope that cannot be achieved by conventional elastomeric seals. The seal design utilizes the controlled application of load to expand the metal seal to achieve a fully formed pressure barrier which allows for the metal-to-metal seal in bores of up to 160% of the original seal diameter.
The metal-to-metal seal has the potential to change the way downhole equipment provides pressure integrity in HPHT environments. In the well servicing market, recent applications of the metal-to-metal seal and the latest lab testing have suggested the prospective of the technology for products in the HPHT arena. Metal-to-metal sealing technology could make well suspensions and intervention possible in hostile HPHT wells that were previously deemed inoperable by the complete removal of elastomers from the design. Ideal for HP/HT applications, metal-to-metal sealing devices can be easily deployed on slickline, electric wireline, coiled tubing, or drill pipe to save operator rig time in areas where cost savings are critical.
Case studies of the high performance characteristics of the metal-to-metal sealing technology in terms of design, testing, and implementation will recognize the alignment to the increased demands of HP/HT applications.
The high expansion arena for bridging devices was revolutionized in the mid 1980s with the introduction of the inflatable type isolation device. In 1986, inflatable type packers and bridge plugs that could be run on coiled tubing through the production tubing were introduced in Prudhoe Bay, Alaska. The inflatable packers and bridge plugs had improved expansion characteristics dictated by the rigors of going through tubing and setting in the casing below without sacrificing pressure holding capability.
By eliminating the workover rig and all ancillary operations required by conventional workovers, through-tubing servicing allowed wells to be returned to production in significantly less time. Inflatable tools have long been valued in completion and workover operations due to their unique ability to expand to several times their diameter and to seal effectively; however, drawbacks to inflatable systems exist in their expansion limitations and differential pressure capabilities at higher temperatures.
In spite of these drawbacks, operators value the ability to perform basic remedial operations while not pulling the production tubing string, and continue to utilize the advantages of high expansion inflatable technology in the well serving market.